Category: Ecosystems

Japanese cherry blossoms make early appearance: Extreme weather to blame

Japanese cherry blossoms make early appearance: Extreme weather to blame

By Georgina Wade

The annual cherry blossom bloom in Japan signals the arrival of spring. Typically occurring in early April, the event brings flocks of tourist to the region looking to experience the floral embodiment of Japan’s most deep-rooted cultural and philosophical beliefs. But never has there been a widespread cherry blossom show put on in the fall – until now. Weathernews received more than 350 reports of early blossoms.

But, what is causing this premature fall bloom? According to the Hiroyuki Wada, an arborist with the Flower Association of Japan, cherry blossom buds develop during summer but usually don’t bloom until because of a plant hormone the leaves release to slow plant growth in preparation for the winter. However, Japan was hit by both Typhoon Jebi and Typhoon Trami in September, which carried powerful winds and salty seawater, forcing trees to shed leaves before the hormone could be released, and with the additional warm air from the South, the trees were ‘tricked’ to blossom.

Category 5 Typhoon Jebi was the strongest storm to hit Japan since 1993, killing 17 people with insured losses estimated at between 2.3 and 4.5 billion USD. A few weeks later, Typhoon Trami followed suit leaving dozens injured and hundreds of thousands of homes without power. Warm air brought about by the typhoons was quickly masked by cooler conditions during the storms’ aftermath, prompting a combination of changeable weather that mimicked spring.

Although it’s clear that this year’s storm season is to blame, the premature cherry blossoming trend has been ongoing for some time. For over 1,000 years, the flowering of Japan’s cherry trees has been chronicled in the city of Kyoto. But bloom dates have shifted radically earlier in recent decades, signalling that the region is warming.

Yasuyuki Ano, a professor of environmental sciences at Osaka Prefecture University, assembled a data set that compiles blossom-flowering dates in Kyoto starting from 800 A.D. Prior to 1850, flowering dates were fairly stable.

But from 1850 to present day, the flowering period has only surged forward at the rate of about one week per century. With warmer March temperatures typically signifying an earlier bloom, scientists believe the earlier bloom dates are directly linked with rising regional temperatures. Both Kyoto’s cherry tree flowering and temperature data suggest that its climate is the warmest it has been in at least a millennium.

The buds that opened now will not be blossoming again in coming spring. Despite this early blooming, experts do not believe this event will disrupt the timing or magnificence of the bloom next spring.

Cover photo by Sora Sagano on Unsplash.
Protecting wetlands helps communities reduce damage from hurricanes and storms

Protecting wetlands helps communities reduce damage from hurricanes and storms

By Siddharth Narayan, University of California, Santa Cruz and Michael Beck, University of California, Santa Cruz

2017 was the worst year on record for hurricane damage in Texas, Florida and the Caribbean from Harvey, Irma and Maria. We had hoped for a reprieve this year, but less than a month after Hurricane Florence devastated communities across the Carolinas, Hurricane Michael has struck Florida.

Coastlines are being developed rapidly and intensely in the United States and worldwide. The population of central and south Florida, for example, has grown by 6 million since 1990. Many of these cities and towns face the brunt of damage from hurricanes. In addition, rapid coastal development is destroying natural ecosystems like marshes, mangroves, oyster reefs and coral reefs – resources that help protect us from catastrophes.

In a unique partnership funded by Lloyd’s of London, we worked with colleagues in academia, environmental organizations and the insurance industry to calculate the financial benefits that coastal wetlands provide by reducing storm surge damages from hurricanes. Our study, published in 2017, found that this function is enormously valuable to local communities. It offers new evidence that protecting natural ecosystems is an effective way to reduce risks from coastal storms and flooding.

Coastal wetlands and flood damage reduction: A collaboration between academia, conservation and the risk industry.

The economic value of flood protection from wetlands

Although there is broad understanding that wetlands can protect coastlines, researchers have not explicitly measured how and where these benefits translate into dollar values in terms of reduced risks to people and property. To answer this question, our group worked with experts who understand risk best: insurers and risk modelers.

Using the industry’s storm surge models, we compared the flooding and property damages that occurred with wetlands present during Hurricane Sandy to the damages that would have occurred if these wetlands were lost. First we compared the extent and severity of flooding during Sandy to the flooding that would have happened in a scenario where all coastal wetlands were lost. Then, using high-resolution data on assets in the flooded locations, we measured the property damages for both simulations. The difference in damages – with wetlands and without – gave us an estimate of damages avoided due to the presence of these ecosystems.

Our paper shows that during Hurricane Sandy in 2012, coastal wetlands prevented more than US$625 million in direct property damages by buffering coasts against its storm surge. Across 12 coastal states from Maine to North Carolina, wetlands and marshes reduced damages by an average of 11 percent.

These benefits varied widely by location at the local and state level. In Maryland, wetlands reduced damages by 30 percent. In highly urban areas like New York and New Jersey, they provided hundreds of millions of dollars in flood protection.

Wetland benefits for flood damage reduction during Sandy (redder areas benefited more from having wetlands). Narayan et al., Nature Scientific Reports 7, 9463 (2017)., CC BY

Wetlands reduced damages in most locations, but not everywhere. In some parts of North Carolina and the Chesapeake Bay, wetlands redirected the surge in ways that protected properties directly behind them, but caused greater flooding to other properties, mainly in front of the marshes. Just as we would not build in front of a seawall or a levee, it is important to be aware of the impacts of building near wetlands.

Wetlands reduce flood losses from storms every year, not just during single catastrophic events. We examined the effects of marshes across 2,000 storms in Barnegat Bay, New Jersey. These marshes reduced flood losses annually by an average of 16 percent, and up to 70 percent in some locations.

Reductions in annual flood losses to properties that have a marsh in front (blue) versus properties that have lost the marshes in front (orange). Narayan et al., Nature Scientific Reports 7, 9463 (2017)., CC BY

In related research, our team has also shown that coastal ecosystems can be highly cost-effective for risk reduction and adaptation along the U.S. Gulf Coast, particularly as part of a portfolio of green (natural) and gray (engineered) solutions.

Reducing risk through conservation

Our research shows that we can measure the reduction in flood risks that coastal ecosystems provide. This is a central concern for the risk and insurance industry and for coastal managers. We have shown that these risk reduction benefits are significant, and that there is a strong case for conserving and protecting our coastal ecosystems.

The next step is to use these benefits to create incentives for wetland conservation and restoration. Homeowners and municipalities could receive reductions on insurance premiums for managing wetlands. Post-storm spending should include more support for this natural infrastructure. And new financial tools such as resilience bonds, which provide incentives for investing in measures that reduce risk, could support wetland restoration efforts too.

Improving long-term resilience

The dense vegetation and shallow waters within wetlands can slow the advance of storm surge and dissipate wave energy. USACE

Increasingly, communities are also beginning to consider ways to improve long-term resilience as they assess their recovery options.

There is often a strong desire to return to the status quo after a disaster. More often than not, this means rebuilding seawalls and concrete barriers. But these structures are expensive, will need constant upgrades as as sea levels rise, and can damage coastal ecosystems.

Even after suffering years of damage, Florida’s mangrove wetlands and coral reefs play crucial roles in protecting the state from hurricane surges and waves. And yet, over the last six decades urban development has eliminated half of Florida’s historic mangrove habitat. Losses are still occurring across the state from the Keys to Tampa Bay and Miami.

Protecting and nurturing these natural first lines of defense could help Florida homeowners reduce property damage during future storms. In the past two years our team has worked with the private sector and government agencies to help translate these risk reduction benefits into action for rebuilding natural defenses.

Across the United States, the Caribbean and Southeast Asia, coastal communities face a crucial question: Can they rebuild in ways that make them better prepared for the next storm, while also conserving the natural resources that make these locations so valuable? Our work shows that the answer is yes.

This is an updated version of an article originally published on Sept. 25, 2017.The Conversation Siddharth Narayan, Postdoctoral Fellow, Coastal Flood Risk, University of California, Santa Cruz and Michael Beck, Research professor, University of California, Santa Cruz. This article is republished from The Conversation under a Creative Commons license. Read the original article.

Cover photo by NPS Everglades/Flickr (public domain)
Australian ecosystems crippling under weight of climate change

Australian ecosystems crippling under weight of climate change

By Georgina Wade

­­Ecosystems across Australia are on the brink of collapse under climate change. Research published in Nature Climate Change analysing the interaction of gradual climate trends and extreme weather events since the turn of the century describes a series of sudden and catastrophic ecosystem shifts that have occurred recently across Australia.

Amongst the most notable tragedies, a mass mortality of corals on the Great Barrier Reef occurred in 2016 after 30% of the reef’s corals died in a relentless nine-month marine heatwave with an additional 20% bleached to death in 2017. And with Australia’s average sea temperature having increased by about 1°C since the start of the 19th century and continuing to climb, the remaining corals face the same fate.

Australia is one of the most climatically variable places in the world. In a study from Environmental Research Letters, Australia showed the highest inter-annual variability of any continent and also showed the highest biome-level variability of any continent for tropical forest, temperature broadleaf forest, and tropical savannas and grasslands.

And despite being a highly populous region involving numerous activities that transform the natural landscape, Australia retains large tracts of near-pristine natural systems.

Many of these regions are iconic, providing benefits to the tourism industry and sustaining outdoor activities while providing precious ecological services. In spite of this, the stress of climate change and extreme weather events is causing environmental alterations in these valuable ecosystems.

The research examined several ecosystems across Australia that have experienced catastrophic changes in the last decade and found that undisturbed systems are not necessarily more resilient to climate change.

Describing a combination of “presses” and “pulses” in which gradual climate change can be thought of as an ongoing “press” on which the “pulse” of extreme events is now superimposed, the case studies provide a range of examples in which both can interact to push an ecosystem to a “tipping point”.

The difficulty in foreseeing the timing and severity of extreme weather events makes predicting ecosystem collapses essentially impossible. Additionally, the cost of targeted interventions can be exorbitant.

Between the uncertainty and associated costs, interventions are difficult to implement and might even require controversial methods like assisted colonisation. Ecosystem management will not only require high policy and philosophy fluidity, but decisions will increasingly need to be made faster and potentially without fully understanding ecological and evolutionary consequences.

Harris, R.M.B et al. (2018). Biological responses to the press and pulse of climate trends and extreme events. Nature Climate Change, Vol. 8, pages 579–587 (2018).

Cover photo Wikimedia Commons (CC BY-SA 3.0): Bleached branching coral (foreground) and normal branching coral (background). Keppel Islands, Great Barrier Reef.
Arctic ice depends on half a degree of heat

Arctic ice depends on half a degree of heat

By Tim Radford

Half a degree Celsius doesn’t sound like much, but for the Arctic ice it could make a world of difference.

Two separate studies have calculated what it would take to keep the Arctic ice frozen through the summer months – and thus preserve the precious polar ecosystem and help contain further global warming.

It’s simple: fulfil the promises that 195 nations made in Paris in 2015, and keep global warming to “well below 2°C” and ideally at 1.5°C by the year 2100.

That extra half a degree makes a huge difference. At a maximum global average warming of 2°C above the norm for most of human history, the Arctic could become technically ice-free once every three to five years.

Reduce carbon dioxide emissions even further, take greater steps to conserve forests and keep the global temperature at the 1.5° C maximum rise, and the chances are that the Arctic seaways will open only about one summer in 40 years.

Glaciologists consider the Arctic “ice-free” when there are only a million square kilometres of floe left. It has yet to happen. But the sea ice has become noticeably thinner, and smaller in surface area, over the last 40 years.

“The good news is that the sea has a quick response time and could theoretically recover if we brought down global temperatures . . . though  other ecosystems could see permanent negative impacts from ice loss”

For more than two decades, meteorologists and oceanographers have repeatedly warned that runaway global warming, as a consequence of ever-greater combustion of fossil fuels, could bring about an ice-free polar ocean by about 2050.

Sea ice is part of the climate machine. It reflects solar radiation and keeps the ocean cool. It provides a surface on which Arctic seals can haul out, and on which polar bears can feed.

But the catch is that, although the world’s nations almost unanimously voted in Paris to contain global warming, the pledges made at the time were nowhere near ambitious enough.

Since the Paris meeting global warming has accelerated, and one group has warned that the 1.5°C limit could be exceeded by 2026. Many researchers think that the political decisions of the next decade will be vital.

Clear benefits

Researchers already know that the 1.5°C target will deliver palpable rewards: it will make a huge difference, for instance, to sea levels, grain harvests and global fish catches.

US and Canadian climate scientists set out to see what difference half a degree would make to the Arctic. They worked with different climate simulations to reach roughly the same conclusion, in two papers in the journal Nature Climate Change.

The Canadian team calculated that at 2°C, ice-free conditions would happen every five years; at 1.5°C, the hazard would drop to one in 40 years; at 3°C, permanent ice-free summers would be likely. A second study from the US backed up the premise.

“I didn’t expect to find that half a degree Celsius would make a big difference, but it really does,” said Alexandra Jahn, of the University of Colorado at Boulder.

Higher costs

“At 1.5°C half the time we stay within our current summer sea ice regime, whereas if we reach two degrees of warming, the summer sea ice will always be below what we have experienced in recent decades.”

Higher levels of warming would impose higher costs: 4°C of warming would deliver a high probability of an ocean free of ice for three months every summer by 2050, and five months a year by 2100.

“The good news is that the sea has a quick response time and could theoretically recover if we brought down global temperatures at any point in the future,” Dr Jahn said.

“In the meantime, though, other ecosystems could see permanent negative impacts from ice loss, and those can’t necessarily bounce back.”

This article was originally published on Climate News Network and can be accessed here.

Cover photo by Anders Jildén on Unsplash.
How will climate change affect Arctic caribou and reindeer?

How will climate change affect Arctic caribou and reindeer?

By Conor Mallory, University of Alberta

This spring, I spent close to two weeks flying over central Nunavut, peering out the window of a small plane at the rolling tundra below, looking for and counting caribou to monitor their numbers.

The Qamanirjuaq barren-ground herd were arriving on their tundra calving grounds to give birth after migrating from winter ranges in the boreal forest. At times caribou dotted the landscape all the way to the horizon.

The terrain here is relatively pristine. There are few communities or developments. Due to the remoteness of the herd’s habitat, it is, in some ways, hard to imagine that human activities — whether climate change or industrial disturbance — could ever be of much concern to them.

And yet, we know that human activity and disturbance provide the most imminent threat to the persistence of many caribou and reindeer populations. (Reindeer and caribou are the same species, Rangifer tarandus, but have different English names in North America and Eurasia. Of course, the species has many names in different languages across the world, such as tuktu in Inuktitut.)

A complicated problem

Just how this iconic Arctic species will be affected in a warming climate remains unclear. Current predictions suggest that the climate will continue to change for decades into the future, regardless of the mitigation actions we take.

Caribou and reindeer have tremendous socioeconomic value in the north, and if we want to maintain sustainable caribou harvesting and husbandry in the future, we must understand how they will respond to environmental change.

My colleagues and I reviewed hundreds of scientific papers that studied caribou and reindeer from Alaska to Nunavut to Russia. By the end, we produced a complete picture of how climate change may affect the caribou and reindeer species, based on current knowledge.

We found that it’s challenging to make general predictions. The species has a circumpolar distribution and inhabits a variety of ecosystems, both similar and distinct. How different populations will respond to varying effects of climate change in this diverse range of systems is complex.

Summer effects

In many regions, climate change is causing longer and warmer summers. In the context of caribou, which live in colder regions, this typically means longer growing seasons and better access to nutritious plants throughout the summer months.

But plants are not the only part of the ecosystem affected by longer and warmer summers. Parasitic flies, particularly warble flies and botflies, torment caribou during the summer months. These insects aren’t just looking for blood like mosquitoes and black flies — they’re trying to lay their eggs on a caribou’s skin or in its nose.

As you can likely imagine, caribou want no part of this. They will spend hours running to escape these parasites, which means they spend less time feeding.

For a given region or herd, will increased plant growth or increase insect harassment have more of an effect on caribou?

We’re already seeing some of these effects play out. In Svalbard, Norway, warmer summers have been generally positive for caribou, as better plant growth has led to heavier animals in the fall. But in Arctic North America, more green growth has been associated with declines in caribou populations, possibly due to the northward expansion of less nutritious shrubs.

Research has shown that insects have been trouble for caribou in Arctic Finland. There, warmer weather brought more insects that harassed caribou calves, which led to less weight gain and more calf deaths.

Winter effects

Winter warming produces similarly complex effects. Climate change is predicted to increase the frequency of winter icing. Icing is usually caused by rain-on-snow or thaw-freeze events, and presents a real problem for caribou.

During the winter caribou dig in the snow to get to food underneath. Icing events trap food beneath an impenetrable layer of ice. These events have led to mass starvation of Arctic caribou and reindeer in the past.

On the other hand, longer autumns and earlier springs shorten the winter period of food scarcity. This should benefit caribou, but the net effect will depend on the balance of these changes in a given region.

These are just some of the wide-ranging potential implications of climate change for Arctic caribou and reindeer. They may also shift their ranges northward and alter their migratory behaviour in response to climate change, or begin sharing their lands with new or increased competitor species such as moose and white-tailed deer.

Importance of caribou and reindeer

Caribou and reindeer provide incredible value throughout the circumpolar world. In ecological terms, they are the most abundant large terrestrial herbivore. They have important grazing effects on plant communities and support predator populations.

The ecological importance of caribou means that changes to caribou and reindeer populations affect many other organisms, including wolves, Arctic shrubs and lichens.

They also have huge socioeconomic value. One report conservatively suggests that three herds in northern Canada provide the equivalent of $20 million dollars annually in food alone. Semi-domesticated reindeer similarly contribute huge value to those who herd them, including the Saami people of Finland, Russia, Norway and Sweden.

If there is a silver lining to this, it’s that we know caribou and reindeer live in a wide variety of environments and ecosystems — and this may provide them with some resilience.

But we don’t know if their ability to adapt is sufficiently agile to respond to the ongoing rapid environmental change in the north.

The ConversationScientists like myself need to work together with wildlife managers and harvesters to unravel the complexity of responses to environmental change. This information will be key to making decisions about caribou going forward.

Conor Mallory, PhD Student, University of Alberta. This article was originally published on The Conversation. Read the original article.

Cover photo by Christopher Michel (CC BY 2.0): Svalbard reindeer.
Reducing flood risk with the help of ecosystems

Reducing flood risk with the help of ecosystems

By Caroline Fouvet

While Houston is still reeling from the impacts of Hurricane Harvey, it appears that one of the city’s main vulnerabilities were its vast impervious surfaces. Concrete, asphalt and various types of surface materials prevent the absorption of water into the soil, and when gallons of rain pour down on urban areas, drainage systems get saturated. Ecosystems could make a substantial contribution to flood risk reduction and enhance urban resilience.

In the case of Hurricane Sandy, a study demonstrated that the presence of marsh wetlands avoided $625 million in direct flood damages across 12 states, as coastal wetlands reduced flood heights. This illustrates that ecosystems can greatly contribute to flood prevention, in particular for low-lying cities. There are different types of ecosystems that can increase cities’ resilience to flooding. However, many of these ecosystems are threatened by human activity, and initiatives are currently being implemented to mainstream their use and strengthen the resilience of low-lying and coastal cities.

Wetlands are diverse and can be found at different locations. For instance, marshes, areas of grassy vegetation and peaty soil, are common in floodplains while tidal wetlands, characterised by reeds, mangroves and mudflats, are located at river mouths. Forested wetlands and ponds are additional wetland types that can absorb large amounts of water runoff and help regulate overland floods. Besides, other forms of ecosystems, such as coral reefs, play an important role in protecting low-lying urban areas. They provide natural barriers against wave energy, an essential aspect to consider when it comes to storm surges and rising sea levels, and act against coastal erosion. Consequently, protecting those ecosystems is essential to leverage the potential flood protection they provide. Wetlands are currently threatened by manmade activities such as new build-up or pasture areas that convert them into non-wetland zones, pollution emanating from untreated wastewater and vegetation clearing. These decrease the wetlands’ capacity to hold back and absorb water.

There currently exist several initiatives that focus on protecting and using those ecosystems against floods. In Bangladesh for example, an initiative funded by the Least Developed Country Fund, focuses on coastal afforestation as a way to increase community resilience. Part of the project is dedicated to planting protective and productive vegetation, including mangroves, to protect communities’ livelihoods from extreme weather events and sea level rise.

The insurance industry is also interested in ecosystems’ capacity to act against flooding. During an event on environmental protection held at the United Nations Office for Disaster Risk Reduction (UNISDR), insurers acknowledged that investments in natural solutions played an important role in risk reduction. Representatives of academia, conservancy institutions and insurers also teamed up to release a study on wetlands’ contribution to reducing floods in the US and included those ecosystems in flood models. Although wetlands are rarely considered in flood risk assessments, the study demonstrated that in high risk areas in New Jersey for instance, “marshes reduce risks to property by as much as 70%” showing the immense impact ecosystems could have on flood risk if managed properly.

Cover photo: U.S. Marine Corps photo by Lance Cpl. Niles Lee/Released (public domain). Marines unload supplies to assist families in Orange, Texas, Sept. 3, 2017. The Marines assisted the Red Cross by transporting supplies from the Red Cross warehouse to families in Orange, Texas, affected by Hurricane Harvey.
Pricing invaluable coral reefs to raise awareness about climate change impacts

Pricing invaluable coral reefs to raise awareness about climate change impacts

By Caroline Fouvet

The Great Barrier Reef (GBR) is one of the world’s most famous natural wonders and attracts over 40 million visitors per year in Australia. Not only is it a powerful emblem for the country, but the GBR also hosts an outstanding ecosystem comprising about 1,500 species of fish, 400 species of coral, 4,000 species of mollusc and some 240 species of birds. What’s more, reefs contribute to coastal hazard risk reduction by buffering wave energy and preventing coastal erosion.

Yet, a combination of threats, spearheaded by climate change, endangers the long-term existence of the GBR and all coral reefs across the globe. On top of water pollution and illegal fishing, the absorption of large CO2 amounts into the ocean severely affects coral reefs. Consequently, a warmer ocean contributes to coral bleaching and spreads infectious diseases while its acidification decreases corals’ growth rates.

To remedy the situation, would putting an economic value on these natural marvels succeed in drawing global attention to the issue? That’s the purpose of a recent Deloitte study that estimated the GBR to be worth $56 billion. This indicative figure captures the GBR’s economic and social value in order to elevate its significance in decision and policy-making. Concrete insights show that the reef contributed 64,000 jobs to the Australian economy in 2015-2016 and that tourism alone derived $29 billion in value.

Although it is hard to assess whether monetising coral reefs has a direct impact on their conservation, tangible figures highlight how environmental preservation is beneficial to human activities and development. So, if we are to price coral reefs, why not also bring in the insurance industry to cover them, as we do for other economic assets? This idea is actually currently being implemented in Mexico, where an insurance scheme has been set up to protect the reef off the Cancún coast. Local tourism-dependent organisations contribute between $1 million to $7.5 million to a collective pot, which will be used to cover storm-induced damages to the reef system.

This scheme, run by Swiss Re and the Nature Conservancy with backing from the Mexican government, illustrates how a public-private partnership can achieve complementary economic and environmental benefits. Trying to understand the economic value of natural resources can help decision makers from the public and business sectors better manage them and improve their resilience to climate change.

However, these approaches are new and the world has already lost half of its coral reefs over the past 30 years. As scientists expect 90% of global corals to be lost by 2050 if no drastic actions are taken, all issues that affect corals in addition to climate change impacts, such as overfishing and run-off from coastal areas, should be seen as priorities now.

Cover photo by Acropora/Wikimedia (CC BY 3.0): Bleached branching coral (foreground) and normal branching coral (background). Keppel Islands, Great Barrier Reef.
Video: Climate change is warming the Arctic faster than other regions

Video: Climate change is warming the Arctic faster than other regions

By Elisa Jiménez Alonso

Channel 4 News Science Editor Tom Clarke travelled to Norway’s Svalbard Islands at the end of last year’s Arctic summer to see the profound effect climate change is having on the (not so) icy North.

The Arctic is warming at a much higher rate than the rest of the Earth putting a fragile ecosystem at risk. Additionally, Arctic ice melt has the potential to have devastating effects around the globe triggering tipping points and intensifying feedback loops that will affect global climate.

Throughout the video a deep rumble can be heard in the background, it is the sound of a crumbling glacier. Tom Clarke’s guide explains, “every year the snowmelt is earlier… wherever I look there is obvious change.” They stand on muddy ground which was once buried underneath a glacier, but that ice has retreaded over a 1km in less than a decade.

Watch the full video to see how disproportionate warming is affecting the Arctic:

Cover photo by NASA/GISS (Public Domain). This image shows trends in mean surface air temperature over the period 1960 to 2011. Notice that the Arctic is red, indicating that the trend over this 50 year period is for an increase in air temperature of more that 2° C (3.6° F) across much of the Arctic, which is larger than for other parts of the globe. The inset shows linear trends over the period by latitude.
Climate change could alter the chemistry of deepwater lakes and harm ecosystems

Climate change could alter the chemistry of deepwater lakes and harm ecosystems

By Alexander L. ForrestUniversity of California, Davis

In an age of rapid global population growth, demand for safe, clean water is constantly increasing. In 2010 the United States alone used 355 billion gallons of water per day. Most of the available fresh water on Earth’s surface is found in lakes, streams and reservoirs, so these water bodies are critical resources.

As a limnologist, I study lakes and other inland waters. This work is challenging and interesting because every lake is an ecosystem that is biologically, chemically and physically unique. They also are extremely sensitive to changes in regional and global weather and long-term climate patterns.

For these reasons, lakes are often called “sentinels of change.” Like the figurative canary in the coal mine, lakes may experience change to their ecosystem dynamics before we start to see shifts in the greater watersheds around them.

In a study I recently co-authored with Goloka Behari Sahoo, S. Geoffrey Schladow, John ReuterRobert Coats and Michael Dettinger, we projected that future climate change scenarios will significantly alter natural mixing processes in Lake Tahoe in the Sierra Nevada range that are critical to the health of the lake’s ecosystem. This could potentially create a condition that we termed “climatic eutrophication.”

While many groups have studied the long-term impact of climate change on lakes, this process can now be added to the growing list of drivers of eutrophication. This is a potentially damaging phenomenon that could affect a number of vital deep-water lakes around the world, degrading water quality and harming fish populations.


The impact of too many nutrients


Eutrophication is a condition that occurs when lakes and reservoirs become overfertilized. Cultural eutrophication is a well-understood process in which lake and reservoir ecosystems become overloaded with chemical nutrients, mainly nitrogen and phosphorus. These nutrients come from human activities, including fertilizer runoff from farms and releases from sewage systems and water treatment plants. Natural weathering processes, atmospheric deposition of air pollutants, and erosion also transport nutrients that are already present in the watershed into the water supply.

Image: A creek in Indiana that has been straightened and deepened to drain farm fields. Agricultural drainage systems can carry large quantities of excess nutrients into rivers, lakes and bays. U.S. Geological Survey

In water bodies, these heavy nutrient loads fertilize algae, causing surface algal blooms. When the algae die, they sink and are broken down as they decompose. This decomposition process consumes dissolved oxygen in the water. As oxygen levels become depleted, hypoxic (dead) zones develop in the bottom waters where oxygen levels are too low to support life. Dead zones harm fisheries and tourism, and algal blooms can contaminate drinking water.

Over the past several decades, state and federal regulators have developed many initiativesto eliminate or reduce nutrient sources. In some cases, such as Seattle’s Lake Washington, water quality has improved through management. In other, larger watersheds – notably, the Great Lakes – nutrient pollution is still a major problem.

Image: Harmful algal bloom in Lake Erie, 2009. T. Archer, NOAA/FlickrCC BY-SA


Climate change and mixing in lakes


As anyone who has swum in a lake knows, the water is typically warmest on the surface where the sun shines on it. Cold water is denser than warmer water, so it sinks. For much of the year, deep lakes will remain stratified (separated into layers).

In fall and late winter, large storms disrupt natural stratification and cause lake waters to overturn. This mixes surface waters down into the lake’s depths and brings deep water up to the surface, where it can absorb oxygen from the atmosphere. This process, which transfers dissolved oxygen from the surface to the lake bottom, is critical for an ecosystem’s health.

Seasonal stratification in temperate lakes. The thermocline is a layer that separates warm water from colder deep water. Hydrated/Wikipedia

But our study showed that surface warming in Lake Tahoe could cause climatic eutrophication by reducing or even ending mixing, thus interrupting the vertical movement of dissolved oxygen from the lake’s surface to the lake bed.

Scientists, spearheaded by the University of California – Davis, have been monitoring conditions at Lake Tahoe for nearly 50 years, so we have good records of short- and long-term changes in water temperatures and quality. Since 1968, the average temperatures of the lake’s surface waters (down to a depth of 80-120 feet) have increased by nearly 0.5 degrees Celsius. That change has increased the lake’s stability – a measurement of how resistant it is to overturning – enough to reduce the probability that surface waters will mix all the way to the lake bottom.

To model possible future conditions, we estimated Lake Tahoe’s annual stability by combining a lake hydrodynamic model – representing how water is moved around the lake – with two different greenhouse gas emission scenarios published by the Intergovernmental Panel on Climate Change. In one scenario, emissions increased rapidly throughout this century; in the other, emissions leveled off by the year 2100.

Under both scenarios, meteorological conditions influencing the lake are projected to change. Notably, wind speeds would decrease by 7-10 percent, and air temperatures would increase by 2.5-4 degrees Celsius. These warmer, less windy conditions across the lake will extend and magnify the warming and stratification trends that we are already seeing.

As the lake remains stratified for longer periods each year and less overturning occurs, dissolved oxygen levels at the bottom will decline. Under these conditions, nutrients stored in the lake bed will be released to the water through chemical reactions that occur in low-oxygen environments. This new source of nutrients, known as internal loading, will further contribute to the process of climatic eutrophication.

Although all lakes are unique ecosystems, this process could also occur in other deep-lake settings around the world, such as Japan’s Lake Biwa or Lake Baikal in southeastern Siberia. Climate change is already shortening the periods each year when many temperate and polar lakes are covered with ice. As water temperatures rise in the upper layers of deep lakes, they will remain stratified for more of the year and will be less subject to mixing. Less dissolved oxygen will be returned to deep waters, which will stress fish populations.

Ice melting on Lake Baikal in Siberia, which contains 20 percent of the fresh water on Earth’s surface. NASA Earth Observatory

And unlike cultural eutrophication, climatic eutrophication could affect entire watersheds or regions, since it is driven by climatic influences rather than by discharges of nutrients into a lake from farms or cities.

Climatic eutrophication has serious implications for long-term water supplies and aquatic ecosystem health around the world. To recognize and track it, we need to identify lakes in North America and around the world that could be at high risk.

The ConversationIn areas where scientists and regulators are working to reduce conventional eutrophication, these experts will also need to factor the possibility of climate-forced eutrophication into their strategies. The first step is to support more monitoring of lakes’ physics and chemistry so that we can recognize, track and predict climatic eutrophication of our lakes and reservoirs.


Alexander L. Forrest, Assistant Professor of Environmental Engineering, University of California, Davis

This article was originally published on The Conversation. Read the original article.


Cover photo by Lara Farhadi (CC by 2.0)
The wide ranging consequences of climate-driven species redistribution

The wide ranging consequences of climate-driven species redistribution

By Gretta PeclUniversity of TasmaniaAdriana VergésUNSWEkaterina PopovaNational Oceanography Centre, and Jan McDonaldUniversity of Tasmania


Last year in Paris, for the very first time, English sparkling wine beat champagne in a blind tasting event. Well established French Champagne houses have started buying fields in Britain to grow grapes, and even the royal family is investing in this new venture. The Conversation

At the same time, coffee-growing regions are shrinking and shifting. Farmers are being forced to move to higher altitudes, as the band in which to grow tasty coffee moves up the mountain.

The evidence that climate change is affecting some of our most prized beverages is simply too great to be ignored. So while British sparkling wine and the beginning of the “coffeepocalypse” were inconceivable just a few decades ago, they are now a reality. It’s unlikely that you’ll find many climate deniers among winemakers and coffee connoisseurs. But there are far greater impacts in store for human society than disruptions to our favourite drinks.

Dramatic examples of climate-mediated change to species distributions are not exceptions; they are fast becoming the rule. As our study published recently in the journal Scienceshows, climate change is driving a universal major redistribution of life on Earth.


Documented and predicted changes in species distribution are occurring all over the globe. Pecl et al. 2017

These changes are already having serious consequences for economic development, livelihoods, food security, human health, and culture. They are even influencing the pace of climate change itself, producing feedbacks to the climate system.

Species on the move

Species have, of course, been on the move since the dawn of life on Earth. The geographical ranges of species are naturally dynamic and fluctuate over time. But the critical issue here is the magnitude and rate of climatic changes for the 21st century, which are comparable to the largest global changes in the past 65 million years. Species have often adapted to changes in their physical environment, but never before have they been expected to do it so fast, and to accommodate so many human needs along the way.

For most species – marine, freshwater, and terrestrial species alike – the first response to rapid changes in climate is a shift in location, to stay within their preferred environmental conditions. On average, species are moving towards the poles at 17km per decade on landand 78km per decade in the ocean. On land, species are also moving to cooler, higher elevations, while in the ocean some fish are venturing deeper in search of cooler water.

Why does it matter?

Different species respond at different rates and to different degrees, with the result that new ecological communities are starting to emerge. Species that had never before interacted are now intermingled, and species that previously depended on one another for food or shelter are forced apart.

This global reshuffling of species can lead to pervasive and often unexpected consequences for both biological and human communities. For example, the range expansion of plant-eating tropical fish can have catastrophic impacts by overgrazing kelp forests, affecting biodiversity and important fisheries.

In wealthier countries these changes will create substantial challenges. For developing countries, the impacts may be devastating.

Knock-on effects

Many changes in species distribution have implications that are immediately obvious, like the spread of disease vectors such as mosquitoes or agricultural pests. However, other changes that may initially appear more subtle can also have great effects via impacting global climate feedbacks.

Mangroves, which store more carbon per unit area than most tropical forests, are moving towards the poles. Spring blooms of microscopic sea algae are projected to weaken and shift into the Arctic Ocean, as the global temperature rises and the seasonal Arctic sea ice retreats. This will change the patterns of “biological carbon sequestration” over Earth’s surface, and may lead to less carbon dioxide being removed from the atmosphere.

Redistribution of the vegetation on land is also expected to influence climate change. With more vegetation, less solar radiation is reflected back into the atmosphere, resulting in further warming. “Greening of the Arctic”, where larger shrubs are taking over from mosses and lichens, is expected to substantially change the reflectivity of the surface.

These changes in the distribution of vegetation are also affecting the culture of Indigenous Arctic communities. The northward growth of shrubs is leading to declines in the low-lying mosses and lichens eaten by caribou and reindeer. The opportunities for Indigenous reindeer herding and hunting are greatly reduced, with economic and cultural implications.

Winners and losers

Not all changes in distribution will be harmful. There will be winners and losers for species, and for the human communities and economic activities that rely on them. For example, coastal fishing communities in northern India are benefiting from the northward shift in the oil sardine’s range. In contrast, skipjack tuna is projected to become less abundant in western areas of the Pacific, where many countries depend on this fishery for economic development and food security.

Local communities can help forge solutions to these challenges. Citizen science initiatives like Redmap are boosting traditional scientific research and can be used as an early indication of how species distributions are changing. Having local communities engaged in such participatory monitoring can also increase the chances of timely and site-specific management interventions.

Even with improved monitoring and communication, we face an enormous challenge in addressing these changes in species distribution, to reduce their adverse impacts and maximise any opportunities. Responses will be needed at all levels of governance.

Internationally, the impacts of species on the move will affect our capacity to achieve virtually all of the United Nations Sustainable Development Goals, including good health, poverty reduction, economic growth, and gender equity.

Currently, these goals do not yet adequately consider effects of climate-driven changes in species distributions. This needs to change if we are to have any chance of achieving them in the future.

National development plans, economic strategies, conservation priorities, and supporting policies and governance arrangements will all need to be recalibrated to reflect the realities of climate change impacts on our natural systems. At the regional and local levels, a range of responses may be needed to enable affected places and communities to survive or thrive under new conditions.

For communities, this might include changed farming, forestry or fishing practices, new health interventions, and, in some cases, alternative livelihoods. Management responses such as relocating coffee production will itself have spillover effects on other communities or natural areas, so adaptation responses may need to anticipate indirect effects and negotiate these trade-offs.

To promote global biodiversity, protected areas will need to be managed to explicitly recognise novel ecological communities, and to promote connectivity across the landscape. For some species, managed relocations or direct interventions may be needed. Our commitment to conservation will need to be reflected in funding levels and priorities.

The success of human societies has always depended on the living components of natural and managed systems. For all our development and modernisation, this hasn’t changed. But human society has yet to appreciate the full implications for life on Earth, including human lives, of our current unprecedented climate-driven species redistribution. Enhanced awareness, supported by appropriate governance, will provide the best chance of minimising negative consequences while maximising opportunities arising from species movements.

Cover photo by Alan Wu (CC by 2.0)