Category: Climate Change Impacts

Ribena hunts for climate-resistant blackcurrants that can cope with Britain’s mild winters

Ribena hunts for climate-resistant blackcurrants that can cope with Britain’s mild winters

By Madeleine Cuff

Cordial maker Ribena is attempting to head off the threat climate change poses to its business by developing a new variety of blackcurrant that can cope with Britain’s increasingly mild winters.

Ribena, which is owned by Lucozade Ribena Suntory, buys up 90 per cent of Britain’s £10m blackcurrant crop each year. But milder winters fuelled by climate change threatens poorer quality, less reliable fruits for its drinks business.

That is why Ribena is investing £500,000 in a five-year project with the James Hutton Institute to develop a new variety of blackcurrant that doesn’t need a cold winter to deliver good summer fruits.

“We are seeing big shifts in our climate. We’ve had an incredibly mild winter, followed by the sunniest May ever, and the driest May in 124 years,” Ribena’s blackcurrant agronomist Harriet Prosser said. “That puts us in a really difficult position.”

Warm winters

Standard blackcurrant varieties need around 2,000 “cold hours” – when the temperature drops below 7C – before they start to bud in the Spring, Ms Prosser explained. The cold spell reduces the risk of frost damage to new buds, and ensures blackcurrant shrubs flower at the right point in the season for peak pollination.

But this year, blackcurrant growers in the UK’s South East saw just 1,300 “cold hours”, raising the risk of lower yields and an unevenly ripened crop.

Long-term threat

Ribena is trying to manage Britain’s unpredictable weather patterns by sourcing blackcurrants from across the country, from Kent to Scotland. Its growers also use a range of varieties, including some better adapted to warmer climates.

But each year growing a bumper crop of blackcurrants in Britain becomes more of a challenge. This year Ribena resorted to using a specially developed nutrient-rich “energy drink” on the plants to encourage fruiting, Ms Prosser said.

Finding a blackcurrant that thrives in Britain’s warming winter conditions is crucial to the sector’s long-term prospects. “I think we would always work to keep British blackcurrants going,” Ms Prosser said. “It would get harder without this breeding programme.”


This article was originally posted on inews.co.uk.
Cover photo by Needpix.
Less rain will fall during Mediterranean winters

Less rain will fall during Mediterranean winters

By Tim Radford

A warmer world should also be a wetter one, but not for the cockpit of much of human history: Mediterranean winters will become increasingly parched. Winter rainfall – and winter is the rainy season – could see a 40% fall in precipitation.

Agriculture and human civilisation began in the Fertile Crescent that runs from eastern Turkey to Iraq: cattle, sheep and goats were domesticated there; the first figs, almonds, grapes and pulses were planted there; the progenitors of wheat were sown there.

Cities were built, irrigation schemes devised, empires rose and fell. Greece colonised the Mediterranean, Rome later controlled it and set the pattern of law and civic government for the next 2000 years in Northern Europe.

Islamic forces brought a different civilisation to the Balkans, North Africa and almost all of Spain. The grain fields of the Nile Valley underwrote the expansion of the Roman Empire.

“What’s really different about the Mediterranean is the geography. You have a big sea enclosed by continents, which doesn’t really occur anywhere else in the world”

But the pressure of history is likely to be affected by the high pressure of summers to come. In a world of rapid climate change, the already dry and sunny enclosed sea will become sunnier and drier, according to two scientists from the Massachusetts Institute of Technology.

They report in the American Meteorological Society’s Journal of Climate that the winter rains that are normally expected to fill the reservoirs and nourish the rich annual harvest from the orchards, vineyards and wheat fields can be expected to diminish significantly, as atmospheric pressures rise, to reduce rainfall by somewhere between 10% and 60%.

Ordinarily, a warmer world should be a wetter one. More water evaporates, and with each degree-rise in temperature the capacity of the air to hold water vapour increases by 7%, to fall inevitably as rain, somewhere.

But episodes of low pressure associated with rain clouds over the Mediterranean become less likely, according to climate simulations. The topography of the landscape and sea determines the probable pattern of the winds.

High pressure grows

“It just happened that the geography of where the Mediterranean is, and where the mountains are, impacts the pattern of air flow high in the atmosphere in a way that creates a high-pressure area over the Mediterranean,” said Alexandre Tuel, one of the authors.

“What’s really different about the Mediterranean compared to other regions is the geography. Basically, you have a big sea enclosed by continents, which doesn’t really occur anywhere else in the world.”

Another factor is the rate of warming: land warms faster than sea. The North African seaboard and the southern fringe of Europe will become 3 to 4°C hotter over the next hundred years. The sea will warm by only 2°C. The difference between land and sea will become smaller, to add to the pattern of high pressure circulation.

“Basically, the difference between the water and the land becomes smaller with time,” Tuel says.

Frequent warnings

Once again, the finding is no surprise: Europe has a long history of drought and flood, but drought tends to leave the more permanent mark. The eastern Mediterranean has already experienced its harshest drought for 900 years and this has been linked to the bitter conflict in Syria.

Researchers have repeatedly warned that the pattern of drought on the continent is likely to intensify, and at considerable economic and human cost.

What is different is that the latest research offers detailed predictions of the nature of change, and identifies the regions likeliest to be worst hit. These include Morocco in north-west Africa, and the eastern Mediterranean of Turkey and the Levant.

“These are areas where we already detect declines in precipitation,” said Elfatih Eltahir, the senior author. “We document from the observed record of precipitation that this eastern part has already experienced a significant decline of precipitation.” 


This article was originally posted on the Climate News Network.
Image: By Mohamed Hozyen, via Wikimedia Commons
Climate impacts outside Europe pose greatest risk to German economy

Climate impacts outside Europe pose greatest risk to German economy

By Will Bugler

European countries that avoid the most severe direct impacts of climate change themselves will not be spared economic damage from climate change, so suggests a new study. The report from the German Environment Agency (UBA), shows that the effects of climate change on countries outside of Europe, pose a much larger risk to Germany’s economy that climate impacts within Europe, because of international trade networks.

COVID-19 has demonstrated clearly the impacts that global systemic risk can have on individual countries’ economies. In a similar way, climate risks that affect one region will cause damage to economies around the world. Globalised trade networks mean that climate risks are therefore shared by all nations. The report’s findings are in line with similar studies from the United Kingdom and Switzerland.

“The effects of foreign trade alone are at least as significant as the economic consequences of climate change within national borders.” The study concludes. Germany and other EU nations, therefore stand to suffer indirectly from the impact of climate change outside the EU.

Countries and regions such as China, India, South and Southeast Asia, the Middle East and Africa are expected to see significant losses in welfare and GDP as a direct result of the impact of climate change on labour productivity, agricultural yields and sea levels.

“The purchasing power of the countries in these regions drops significantly compared to the reference trend without climate change, with considerable indirect negative consequences for Germany as a trading partner,” the study states.

The researchers note, however, that the transnational effects of global climate change cannot simply be cushioned by a general reduction in international trade relations. Such a move could not only lead to significant losses in prosperity in Germany, but also to a disruption in the worldwide production of goods and services and “networking that is central to the social and political stability of the world”, the researchers point out.

Instead, the study recommends that the resilience of the German economy “be improved through greater diversification or restructuring of global trade relations. This must be accompanied by targeted support for adaptation measures in the severely affected regions of the world, which are important for Germany in terms of supply and sales markets and are difficult to substitute”.

Download a copy of the report here [German].


Cover photo by  Markus Spiske on Unsplash.
First ever climate assessment for India region projects intense heat and extreme rainfall

First ever climate assessment for India region projects intense heat and extreme rainfall

By Will Bugler

The first ever regional climate assessment for the India region, to be published later this month, suggests that India must prepare for a hooter climate, characterised by extreme heat and floods. The scientific study projects that  by the end of the century, the average temperature in India will rise by around 4.5˚C, heat waves will 3-4 times more frequent, sea levels will rise by 30 cm and the intensity of tropical cyclones will increase substantially.

The study will be an open access release on July 1st. It looks in detail at the impact of climate change on the regional monsoon, the Indian Ocean and the Himalayas. It also examines the regional climate change projections based on the climate models used by the IPCC Fifth Assessment Report (AR5) and national climate change modelling studies.

The study provides a more detailed assessment of the regional impacts of climate change compared with the global IPCC Assessment reports which are typically published every 6-7 years. The study will provide a detailed analysis of future climate effects over the Indian subcontinent, especially relating to the Indian monsoon and other locally significant climatic phenomena.

Click here to read the report.


Cover photo by Mike Sangma on Unsplash.
Siberia dries out as forests burn and climate heats

Siberia dries out as forests burn and climate heats

By Kieran Cooke

Residents of the small Arctic town of Khatanga have never experienced anything like it: their home is changing at a gallop as Siberia dries out.

Khatanga – population around 3,500 – is well north of the Arctic Circle, with usual daytime temperatures at this time of year hovering round a chilly 0°C. On 22 May the temperature in the town reached 25°C – more than double the record to date.

Global warming is causing profound change across the Arctic, a region which acts like a giant air conditioning system regulating the Earth’s climate.

Temperatures are rising far faster than elsewhere: sea ice cover is rapidly disappearing, valuable fish stocks are moving ever further north in search of colder waters, land around the Arctic perimeter is drying out – particularly across the vast expanse of Siberia.

Permafrost is melting. This week a giant oil tank collapsed and ruptured at a nickel and palladium works near the city of Norilsk in northern Siberia, spilling thousands of tonnes of diesel into the nearby Ambarnaya river.

Worst for years

The storage tank is believed to have been built on permafrost: a state of emergency has been declared for what is being described as one of the worst environmental disasters in recent Russian history. State media say an area stretching over 350 square kilometres is polluted and will take years to clean up.

A series of wildfires, often enveloping hundreds of thousands of hectares of Siberia’s boreal forests, or taiga, have raged in many areas over recent weeks.

In early spring farmers across Siberia often light fires to clear land of dead grass and unwanted vegetation. A combination of high temperatures and strong winds has led to fires blazing out of control. Last year Siberia’s fires are estimated to have destroyed an area of forest the size of Belgium.

“2019 saw a record number of fires over the summer months in Siberia”, says Thomas Smith, an environmental geographer at the London School of Economics (LSE) and a wildfires expert.

“This year, aided by high temperatures and conditions that have promoted growth, the fires started early, though so far their incidence is about average and not as extensive as in 2019.

“Forest fires in this region of the Arctic used to happen about every hundred years and now we’re seeing them every summer”

“But what’s important are the peak summer months: the soils are dry and there’s plenty of fuel, so conditions are favourable for more widespread fires”, Dr Smith told Climate News Network.

One of the regions worst affected is in the south of Siberia, around Lake Baikal, the world’s largest and deepest freshwater lake, where an estimated half a million hectares of forest were destroyed by fire earlier this year.

Evgeny Zinichev, Russia’s emergencies minister, speaks of a critical situation unfolding in Siberia and across Russia’s Far East. “The main reason, of course, is unauthorised and uncontrolled agricultural fires”, he says.

“A less snowy winter, an abnormal winter, and insufficient soil moisture are factors that create the conditions for the transition of landscape fires to settlements.”

Other factors have also led to the spread of wildfires. After weeks of lockdown due to the Covid-19 pandemic, people trapped in often cramped and stiflingly hot apartment blocks have sought freedom in the countryside and forests, camping and lighting barbecues.

Hungry Chinese demand

In Soviet times the taiga was more closely monitored and policed: that system has tended to break down in recent years. The Covid crisis has also drawn attention away from the fires.

Corruption and illegal logging, driven in large part by China’s demand for forest products, is an additional threat to the taiga.

The warming and wildfires are having an impact not only across Siberia but around the world. Its forests act as an enormous carbon sink, storing millions of tonnes of climate-changing greenhouse gases.

Fires and logging release the gases into the atmosphere, creating what scientists call a positive feedback loop – the more gases that are released, the warmer and drier the air becomes, so that more areas of forest are at risk from fire.

“Substantial areas of forest in Siberia are on peat soils”, says Dr Smith. “When these soils dry out, fires go underground, threatening to release large amounts of carbon which can lead to a catastrophic climate event.”

Wide impact

Smoke from the fires is carried by winds to other parts of the globe, trapping warm air near the Earth’s surface. The warm air generated by the fires is also likely to result in a further depletion in ice cover and warming of the Arctic seas.

The temperature rises and the growing incidence of wildfires in Siberia have other effects too.

A recent study published in the journal Scientific Reports says the fires mean that more nutrients, particularly nitrogen, leak into streams and waterways.

“Forest fires in this region of the Arctic used to happen about every hundred years and now we’re seeing them every summer”, says Bianca Rodriguez-Cardona, of the University of New Hampshire, Durham, US, one of the study’s authors.

“This increase in fires leads to more input of inorganic solutes into local streams which can alter the chemistry and trigger issues like increased algal blooms and bacteria that can be harmful to humans who depend on these waterways for drinking water, fishing and their livelihoods.” When these waters reach the Arctic they can also dramatically alter the chemistry of the surrounding seas, says the study. – Climate News Network


This article was originally posted on the Climate News Network.
Cover photo: The Siberian taiga blazes as petroleum gas burns off in a flare. Image: By Copper Kettle, via Wikimedia Commons
Gender lens essential to addressing linked climate change and security crises, urges joint UN report

Gender lens essential to addressing linked climate change and security crises, urges joint UN report

Nairobi and New York – 9 June 2020 – As countries reel from the devastating social and economic impacts of the COVID-19 pandemic, gender inequality is shaping the experience of crisis, as well as prospects for resilience and recovery.

A new report – Gender, Climate & Security: Sustaining Inclusive Peace on the Frontlines of Climate Change – by the UN Environment Programme (UNEP), UN Women, the UN Development Programme (UNDP), and the UN Department of Political and Peacebuilding Affairs (UNDPPA) reveals the close links between gender, climate, and security, and shows that women on the frontlines of climate action are playing a vital role in conflict prevention and sustainable, inclusive peace.

Communities affected by conflict and climate change face a double crisis. The pandemic further compounds the impacts of climate change on food security, livelihoods, social cohesion, and security. This can undermine development gains, escalate violence and also disrupt fragile peace processes.

Women and girls are facing disproportionate economic burdens due to different types of marginalization; gendered expectations can lead men and women to resort to violence when traditional livelihoods fail; and important socio-economic shifts can result from changes to patterns of migration.

“Unequal access to land tenure, financial resources, and decision-making power can create economic stress for entire households in times of crisis, leaving women disproportionately exposed to climate-related security risk,” said UNEP’s Executive Director, Inger Andersen. “The climate crisis stretches well beyond just climate, and tackling it effectively requires responses that address the links between gender, climate and security –we must ensure no one is left behind.”

Research supporting the report shows that in Chad, gender-based violence and structural inequality limit the capacity of communities to adapt to climate shocks. In Sudan, the growing scarcity of fertile land caused by extended droughts and rainfall fluctuation is marked by increases in local conflict between farmers and nomadic groups. Many people –mostly men– have migrated away from local villages in search of alternative livelihoods in large agricultural schemes or in nearby mines, leaving women with greater economic burdens. Other examples highlight climate-related security risks for women in urban areas, especially within informal settlements. Research from Pakistan and Sierra Leone suggest that water shortages, heat waves, and extreme weather events can create new risks of gender-based violence and deepen pervasive inequalities.

The report makes clear the urgent need for gender-responsive action to tackle these linked crises. Interventions around natural resources, the environment and climate change, for example, provide significant opportunities for women’s political and economic leadership, and strengthen their contributions to peace. Sustainable natural resource programming also offers opportunities to mitigate sexual and gender-based violence in conflict. Recognizing that peace and security, human rights, and development are interdependent is vital to forge a better future, the report argues.

“Gender inequality, climate vulnerability, and state fragility are strongly interlinked –we know, for example, that countries with higher values in one of these areas tend to score higher in the other two”, said UNDP Administrator Achim Steiner. “At the same time, aid targeting initiatives that empower women and promote gender equality remains very low. The concrete examples of these types of initiatives in action showcased in this report can help spur further research and inspire more opportunities to reinforce the roles of women in peacebuilding, which is fundamental to help us achieve the Sustainable Development Goals.”

“Strengthening the role of women in the management of natural resources also creates opportunities for them to act as peacebuilders and manage conflicts in non-violent manners,” adds Oscar Fernández-Taranco, Assistant Secretary-General for Peacebuilding Support.

Gender considerations should also be fully reflected in emerging policy and programming on climate-related security risks –not only to strengthen awareness and understanding of particular vulnerabilities, but also to highlight opportunities for leadership and inclusion of women and marginalized groups in decision-making processes.

More investment for gender equality and women’s empowerment is required in fragile states, including implications on human mobility, and especially in sectors related to natural resources, where it is particularly low.

“Building back better with a gender lens means ensuring our post-COVID economies tackle the fundamental inequalities in society and end violence against women,” said UN Women Executive Director, Phumzile Mlambo-Ngcuka. “Women are a powerful force to rebuild societies more securely, from providing food and shelter, to generating vital income and leading sustainable change.”

Read the report here.


This article was accessed via PreventionWeb. Read the original article here.
Cover photo by Ninno JackJr on Unsplash.
Letting rivers run wild could reduce UK flooding – new research

Letting rivers run wild could reduce UK flooding – new research

By Neil Entwistle and George Heritage

The UK government currently spends £2.6 billion on flood defences in England, and that amount is set to double by 2026. Flooding in February 2020 showed how that’s likely to be a good investment, as climate change drives warmer and wetter weather each winter. But when it comes to managing rivers to prevent flooding in towns and cities downstream, we’re often our own worst enemy.

After the second world war, Britain embarked on a mission to reconstruct its rivers. Workers cut ditches to drain moorland, making it suitable for livestock farming. Looping rivers which once wound lazily through floodplains – flooding these areas once every two years or so – were straightened into rigid channels. River beds were dredged to deepen them and banks excavated to make them steeper, an unnatural situation that takes routine management to maintain.

The idea behind all of this was to reduce flooding by increasing the speed at which water moves downstream. But this also increased the power of rivers to move sediment. Gravels and cobbles dash along these modified and heavily managed rivers, accumulating where the water slows down, as it moves through towns and cities. Here, the river bed swells as sediment piles up, increasing local flood risk.

Flooding in Carlisle, December 2015. Environment Agency geomatics group, Author provided

Over 60% of the UK’s watercourses have been transformed in this way, changing the fundamental character of many British rivers – and the natural processes that would usually govern them – over just a few generations. In a new study, we found that doing nothing is often a better course of action for reducing flooding than these heavy handed attempts to mechanically alter rivers.

Going with the flow

We studied the River Caldew in Cumbria, which has caused three major floods in nearby Carlisle since 2010. Satellite data showed that straightening, deepening and embanking was common along the river between 2005 and 2016. Very little sediment was spotted in the river and across the floodplain, suggesting that almost all of it was being funnelled downstream towards Carlisle.

During this time, the channel through the city was widened in the hope that this would cause flood water to spread out and lose energy. But this only increased the problem of sediment building up within the river, creating a shallower channel through Carlisle that’s prone to overflowing.

A stretch of the Caldew near Mosedale in 2003. The channel is fairly rigid and surrounded by managed grassland. Google Earth, Author provided

Outside of the city, in parts where maintenance has been relaxed, the river has begun to return to a more natural state. Multiple “wandering” channels can now be seen alongside wide areas of deposited gravel. This is encouraging, as it suggests that the main river and its floodplain are reconnecting, allowing the sediment it transports to fall out of the channel and collect upstream.

We found that rivers which are allowed to behave more naturally are better at locking up sediment upstream, rather than letting it accumulate in unnaturally high quantities in flood-prone towns and cities. If more rivers are allowed to behave naturally and develop this way, it could help reduce future flooding.

The Caldew at Cummersdale in 2018. Note the variety of vegetation and increased gravel. Google Earth, Author provided

This hands-off approach to managing rivers is also much cheaper than hard engineering and brings a wealth of environmental benefits with it. The wandering channel system that’s evolving on the River Caldew has the greatest variety of features and habitats across the entire watercourse.

There are gravel bars, deep pools, floodplain wetlands, ponds and river cliffs. This diversity provides greater spawning habitat for fish, and cooler refuges for their fry. The open water habitats benefit amphibians, the trees and shrubs help kingfisher hunt and sand martins can nest in the river cliffs. Beetles and spiders scurry in the shingle, earning this wilder stretch of the Caldew a designation as a site of special scientific interest.

The last 75 years have seen many UK rivers change beyond recognition. The way we manage them in future must look very different. Relaxing our iron grip and allowing natural processes to flourish on rivers once more could be our best hope for reducing flooding, while reviving lost ecosystems rich in native wildlife.


This article was originally posted on The Conversation.

Cover photo from Wikimedia Commons.

3 billion people may face Saharan heat levels by 2070

3 billion people may face Saharan heat levels by 2070

By Tim Radford

If humans go on burning ever more fossil fuels to put ever higher concentrations of greenhouse gases into the atmosphere, then one third of the world’s population may face – within 50 years – heat levels that could be all but intolerable.

By 2070, 19% of the land area of the planet, home to 3.5 billion people, could be faced with a mean annual temperature of 29°C. That is, although there would be seasons in which temperatures fell well below this average, these would be followed by summers in which the thermometer went much higher.

Right now, only 0.8% of the land surface of the planet experiences such a mean annual temperature, and most of this space is located in the Saharan desert region of North Africa. But population growth – already highest in the poorest and hottest parts of the globe – and the projected increases in planetary average temperatures will expand this danger zone to almost one fifth of the planet’s land area, to embrace a third of the world’s people.

The conclusion – published in the Proceedings of the National Academy of Sciences – sounds like a dramatic advance on repeated warnings that planetary average temperatures could be 3°C above the long-term average for almost all of human history. But it may not be.

One important difference is that climate science forecasts tend to describe the entire planet. But almost three fourths of the planet is ocean, which is warming much more slowly than the land surfaces. Another is that climate forecasts predict average change for a sphere with a circumference of 40,000 kms. And the third factor is that such predictions do not specifically address where humans choose to live.

“Our computations show that each degree of warming above present levels corresponds to roughly one billion people falling outside of the climate niche”

Xu Chi of Nanjing University in China and his European co-authors started from the premise that humans – like all animal species – have a preferred climate niche. They looked back through 6000 years of the history of civilisation and concluded that most of humankind flourished within a climate space between annual averages of 11°C and 15°C. A much smaller number of people lived in places where the average temperature was between 20°C and 25°C.

And they found that – although civilisations rose and fell, whole peoples disappeared, wars, plagues and famines struck, and entire populations migrated to or invaded other homes – nearly all of humankind continued to prefer to live in land zones at between 11°C and 15°C.

“This strikingly constant climate niche likely represents fundamental constraints on what humans need to survive and thrive,” said Marten Scheffer of Wageningen University in the Netherlands.

But in the next 50 years, the average temperature experienced by an average human is expected to rise by 7.5°C. And because population growth is highest in the already hottest regions, these temperature rises will affect more and more people.

Warnings mount

By 2070 this total could reach 3.5bn people, across 19% of the planet’s land surface, many of them exposed to temperatures and climate conditions that right now would be considered difficult to survive.

In just the last six or seven weeks, climate scientists have warned that rising temperatures present a direct threat to the natural ecosystems on which human civilisation depends; that the number of days that US farmworkers will find dangerously hot will almost double; that potentially lethal combinations of heat and humidity trailed as a future hazard may already have arrived, in limited locations for brief periods; that some will find more heat brings more extremes of rainfall, while other regions will become increasingly arid; and that South Asia, in particular, is at increasing hazard from ever more extreme temperatures and choking pollution, thanks to global climate change.

But the latest attempt to look at the big picture trumps all of these already bleak findings. As usual, other climate researchers will question their assumptions and challenge their conclusions, but the authors are fairly sure of their ground.

“We were frankly blown away by our initial results,” said Dr Xu. “As our findings were striking, we took an extra year to carefully check all assumptions and computations. We also decided to publish all data and computer codes for transparency and to facilitate follow-up work by others.

“The results are as important to China as they are to any other nation. Clearly we will need a global approach to safeguard our children against the potentially enormous social tensions the projected change could invoke.”

Range of pressures

This also raises issues already repeatedly raised by climate forecasters: the people most threatened by climate change are already among the world’s poorest. So there will be pressure to migrate. And there will be potential for conflict.

What will happen in the next 50 years under circumstances in which governments go on authorising fossil fuel consumption is difficult to predict with any certainty. Communities will to a certain extent adapt. Economic development could help contain some of the challenges. And governments could decide to act.

“The good news is that these impacts can be greatly reduced if humanity succeeds in curbing global warming,” said Tim Lenton, of Exeter University in the UK.

“Our computations show that each degree of warming above present levels corresponds to roughly one billion people falling outside of the climate niche.”


This article was originally posted on the Climate News Network.
Cover photo by Tomáš Malík on Unsplash
We found 2˚C of warming will push most tropical rainforests above their safe ‘heat threshold’

We found 2˚C of warming will push most tropical rainforests above their safe ‘heat threshold’

By Aida Cuní Sanchez and Martin Sullivan

As they photosynthesise and grow, tropical forests remove enormous amounts of carbon from the atmosphere, reducing global warming. However, forests are also themselves affected by this warming. If it gets too hot or too dry, trees will grow less and may start to die faster, decomposing and releasing that carbon back into the atmosphere.

This is why scientists like us are concerned that climate change will mean death outweighs growth, and tropical forests will eventually switch to releasing more carbon into the atmosphere than they take out. Our new research, published in the journal Science, shows that tropical forests can resist small increases in temperature – but only up to a point.

Such forests are found right across the tropics and although they’re generally hot and wet, this simplification hides a lot of variation in climate. Some forests at the southern edge of the Amazon reach 35˚C in the hottest months of the year, while others towards the foothills of the Andes reach no more than 26˚C. The jungles of the western Amazon and Borneo are wet all year round, while elsewhere in Amazonia and in Africa there are “rainforests” that have virtually no rainfall in the driest months. We used this variation to understand how climate affects the amount of carbon tropical forests store, and to predict how this might change in the future.

Why did we look at variation between locations to predict changes over time? Because, since individual trees live for a long time, even decades of monitoring cannot tell us exactly how a forest will respond to climate change in the long term. For example, Amazonian forests that are drying fastest are slowly shifting towards more drought-adapted tree species, but this is only evident if we look at the youngest trees.

Measuring trees in Ndoubale-Ndoki National Park, Congo. Aida Cuni Sanchez, Author provided

Looking at variations between different tropical forests gives us a unique perspective on how tropical forests might respond to future climatic conditions, as we can observe how forests grow in a particular climate after having had time to adapt. For example, we can use the difference in the amount of carbon stored by forests growing at 30˚C and 32˚C as a guide for how the former might respond over the long-term to a 2˚C increase in temperature.

So, we joined efforts with 223 other researchers. The international team measured more than half a million trees in 813 forests across the tropics. In each forest patch we recorded tree diameter, species and height. And a few years later we went back to measure how much each tree had grown, if some had died, or if new ones had established. Each tree had a numerical tag, which allowed us to track them over their lives. Overall we identified about 10,000 tree species and made two million measurements of diameter, across 24 tropical countries.

We found that tropical forests can tolerate small changes in temperatures, but only up to a point. Once annual mean daytime temperatures in the warmest part of the year hit 32˚C or more, these forests release four times as much carbon to the atmosphere per degree increase in temperature as they would below the threshold. This is mostly because hotter temperatures reduce tree growth, but it’s also down to heat combined with drought meaning trees are more likely to die and decompose, which releases carbon back into the atmosphere.

Adaptation is possible – if we act now

Our results indicate that we have an opportunity to ensure forests can adapt to climate change, but we need to act now. Firstly, we need to protect and connect the forests that remain, so that tree species are able to move as the climate warms.

But trees go from place to place very slowly: they can only “move” when animals or the wind carry their seeds somewhere else where climatic conditions are suitable. The more fragmented the forests, the less likely seeds can reach certain patches. Also, smaller patches are more affected by “edge effects” such as increased light, drier air and fire risks, creating challenging conditions for seeds to germinate and grow. Therefore, keeping forests connected is of crucial importance.

The researchers behind the new study made more than 2 million tree measurements. Aida Cuni Sanchez, Author provided

Secondly, we need to limit emissions. Even limiting global temperatures to 2°C above pre-industrial levels – already a best case scenario – will push nearly three-quarters of tropical forests above the 32°C heat threshold we identify. As each degree increase above the heat threshold releases 100 billion tonnes of CO₂ from tropical forests to the atmosphere, representing over 280 years of annual fossil fuel emissions by a country such as the UK, there is a clear incentive to avoid further warming.

Of course, reducing emissions is challenging. However, right now, humanity has a unique opportunity. During the current pandemic, emissions from transport, among other sectors, have been significantly reduced. So this shows that we humans can do it. We can design a healthier cooler future for all of us: rainforests and humans.


This article was originally posted on The Conversation.
Cover photo by Lingchor on Unsplash
South Asia’s twin threat: extreme heat and foul air

South Asia’s twin threat: extreme heat and foul air

By Tim Radford

Extreme heat can kill. Air pollution can seriously shorten human lives. By 2050, extreme summer heat will threaten about 2 billion people on and around the Indian sub-continent for around 78 days every year. And the chances of unbearable heat waves and choking atmospheric chemistry at the same time will rise by 175%.

Climate scientists have been warning for decades that what were once rare events – for instance the 2003 heat wave that claimed tens of thousands of lives in Europe – will, as global average temperatures rise, become the new normal.

And they have repeatedly warned that in step with extreme summer temperatures, extreme humidity is also likely to increase in some regions, and to levels that could prove potentially fatal for outdoor workers and people in crowded cities.

The link between air pollution and ill health was established 60 or more years ago and has been confirmed again and again with mortality statistics.

Risk to megacities

Now a team from China and the US confirms once more in the journal  AGU Advances, published by the American Geophysical Union, that the danger is real, and that they can tell where it is becoming immediate: in seven nations that stretch from Afghanistan to Myanmar, and from Nepal to the tip of southern India.

Around 1.5bn people live there now, and they are already learning to live with around 45 days of extreme heat every year. By 2050, there will be 2bn people, most of them crammed into megacities in Afghanistan, Bangladesh, Bhutan, India, Myanmar, Nepal and Pakistan, and climate models confirm that the number of days of extreme heat could rise to 78 a year.

The number of days on which cities – already blighted by air pollution – reach health-threatening levels of high particulate matter will also rise. When heat and choking air chemistry become too much, lives will be at risk.

That extremes of summer heat are on the increase is now a given. That the intensity, duration and frequency of heat waves will go on rising has also been established. Extremes of heat are a threat to crops and a particular hazard in cities already much hotter than their surrounding landscapes.

“South Asia is a hotspot for future climate change impacts. Much research is needed over other parts of the world on  the risks they pose, and their potential human health effects”

One research group has identified 27 ways in which high temperatures can kill. Others have repeatedly warned of the dangerous mix of high temperatures and high humidity (climate scientists call it the “wet bulb” temperature), and one team of scientists has already argued that such conditions have already arrived, albeit so far for short periods and in limited locations.

The researchers chose the so-called wet-bulb temperature of 25°C as their threshold for an unhealthy extreme, and then worked out the number of days a year that such conditions happened in South Asia: between 1994 and 2006, these arrived at an average of between 40 and 50 days a year.

They then looked at the likely rise with forecast increases in average planetary temperature, depending on how vigorously or feebly the world’s nations tried to switch from fossil fuels to renewable energy sources. The probability increased by 75%.

They then chose widely-agreed dangerous thresholds for air pollution with soot, and sulphate aerosols, usually from fossil fuel combustion, to find that extremes of pollution would happen by 2050 on around 132 days a year.

Tenfold risk increase

Then they tried to estimate the probabilities that extreme pollution and extreme heat would coincide. They judged that the frequency of these more than usually hazardous days would rise by 175%, and they would last an estimated 79% longer. The area of land exposed to this double assault on human health would by then have increased tenfold.

Scientific publications usually avoid emotional language, but the researchers call their own finding “alarming.”

“South Asia is a hotspot for future climate change impacts,” said Yangyang Xu, of Texas A&M University, the first author.

“I think this study raises a lot of important concerns, and much research is needed over other parts of the world on these compounded extremes, the risks they pose, and their potential human health effects.”


This article was originally published on the Climate News Network.
Cover photo by Alice Yamamura