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Deforestation can raise local temperatures by up to 4.5℃ – and heat untouched areas 6km away

<p>Forests directly cool the planet, like natural evaporative air conditioners. So what happens when you cut them down?</p> <p>In tropical countries such as Indonesia, Brazil and the Congo, rapid deforestation <a href="https://www.nature.com/articles/nclimate3250">may have accounted for</a> up to 75% of the observed surface warming between 1950 and 2010. <a href="https://iopscience.iop.org/article/10.1088/1748-9326/ac2fdc">Our new research</a> took a closer look at this phenomenon.</p> <p>Using satellite data over Indonesia, Malaysia and Papua New Guinea, we found deforestation can heat a local area by as much as 4.5℃, and can even raise temperatures in undisturbed forests up to 6km away.</p> <p>More than 40% of the world’s population live in the tropics and, under climate change, rising heat and humidity could push them into <a href="https://www.nature.com/articles/s41561-021-00695-3">lethal conditions</a>. Keeping forests intact is vital to protect those who live in and around them as the planet warms.</p> <p><a href="https://images.theconversation.com/files/431859/original/file-20211115-13-g3akke.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img src="https://images.theconversation.com/files/431859/original/file-20211115-13-g3akke.jpg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt="" /></a> <span class="caption">Trees provide shade, habitat, and regulate the supply of clean water.</span> <span class="attribution"><span class="source">Shutterstock</span></span></p> <h2>Deforestation hot spots</h2> <p>At the recent climate change summit in Glasgow, world leaders representing 85% of Earth’s remaining forests committed to ending, and reversing, <a href="https://ukcop26.org/glasgow-leaders-declaration-on-forests-and-land-use/">deforestation by 2030</a>.</p> <p>This is a crucial measure in our fight to stop the planet warming beyond the internationally agreed limit of 1.5℃, because forests store vast amounts of carbon. Deforestation releases this carbon – <a href="https://royalsocietypublishing.org/doi/full/10.1098/rstb.2019.0120">approximately 5.2</a> billion tonnes of carbon dioxide per year – back into the atmosphere. This accounts for nearly 10% of the global emissions from 2009-2016.</p> <p>Deforestation is <a href="https://www.science.org/doi/10.1126/sciadv.aax8574">particularly prevalent</a> in Southeast Asia. <a href="https://data.globalforestwatch.org/documents/14228e6347c44f5691572169e9e107ad/explore">We calculate</a> that between 2000 and 2019, Indonesia lost 17% of its forested area (26.8 million hectares of land), and Malaysia 28% of its forest cover (8.12 million hectares). Others in the region, such as Papua New Guinea, are considered “<a href="https://wwf.panda.org/discover/our_focus/forests_practice/deforestation_fronts_/">deforestation hot spots</a>”, as they’re at high risk of losing their forest cover in the coming decade.</p> <p>Forests in this region are cut down for a variety of reasons, including for expanding palm oil and timber plantations, logging, mining and small-scale farms. And these new types of land uses produce different spatial patterns of forest loss, which we can see and measure using satellites.</p> <h2>What we found</h2> <p>We already know forests cool the climate directly, and losing forest causes local temperatures to rise. But we wanted to learn whether the different patterns of forest loss influenced how much temperatures increased by, and how far warming spread from the deforested site into neighbouring, unchanged areas.</p> <p>To find out, <a href="https://iopscience.iop.org/article/10.1088/1748-9326/ac2fdc">we used</a> satellite images that measure the temperature of the land surface. As the illustration below shows, we measured this by averaging forest loss in rings of different widths and radius, and looking at the average temperature change of the forest inside the ring.</p> <p><a href="https://images.theconversation.com/files/431019/original/file-20211109-27-mpcx2l.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img src="https://images.theconversation.com/files/431019/original/file-20211109-27-mpcx2l.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt="Illustration of how temperature changes due to forest loss." /></a> <span class="caption">How forest clearing near an unchanged area causes temperatures to rise.</span></p> <p>For example, if you consider a circle of forest that’s 4km wide, and there’s a completely deforested, 2km-wide ring around it, the inner circle would warm on average by 1.2℃.</p> <p>The closer the forest loss, the higher the warming. If the ring was 1-2km away, the circle would warm by 3.1℃, while at 4-6km away, it’s 0.75℃.</p> <p>These might not sound like big increases in temperature, but global studies show <a href="https://www.pnas.org/content/114/35/9326.short">for each 1℃ increase in temperature</a>, yields of major crops would decline by around 3-7%. Retaining forest within 1km of agricultural land in Southeast Asia could therefore avoid crop losses of 10-20%.</p> <p>These estimates are conservative, because we only measured the effect of forest loss on average yearly temperatures. But another important factor is that higher average temperatures <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2011JD016382">usually create</a> higher temperature extremes, like those during heatwaves. And those really high temperatures in heatwaves are what put people and crops at most risk.</p> <p>Of course, forests aren’t normally cut down in rings. This analysis was designed to exclude other causes of temperature change, putting the effect of non-local forest loss in focus.</p> <h2>Why is this happening?</h2> <p>Forests cool the land because trees draw water from the soil to their leaves, where it then evaporates. The energy needed to evaporate the water comes from sunshine and heat in the air, the same reason you feel colder when you get out of a pool with water on your skin.</p> <p>A single tree in a tropical forest can cause <a href="https://www.sciencedirect.com/science/article/pii/S0959378017300134">local surface cooling equivalent</a> to 70 kilowatt hours for every 100 litres of water used from the soil — as much cooling as two household air conditioners.</p> <p>Forests are particularly good at cooling the land because their canopies have large surface area, which can evaporate a lot of water. When forests in tropical regions are cut down, this evaporative cooling stops, and the land surface warms up.</p> <p>This is not news to the people of Borneo. In 2018, researchers surveyed <a href="https://www.sciencedirect.com/science/article/pii/S0959378017314188">people in 477 villages</a>, and found they’re well aware nearby forest loss has caused them to live with hotter temperatures. When asked why forests were important to their health and the health of their families, the ability for trees to regulate temperature was the most frequent response.</p> <p><a href="https://images.theconversation.com/files/431029/original/file-20211109-13-18wfaj.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=1000&amp;fit=clip"><img src="https://images.theconversation.com/files/431029/original/file-20211109-13-18wfaj.jpeg?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt="Logging road" /></a> <span class="caption">A logging road in East Kalimantan, Bornea: logged forest on the left, virgin/primary forest on the right.</span> <span class="attribution"><a href="https://upload.wikimedia.org/wikipedia/commons/a/ab/Logging_road_East_Kalimantan_2005.jpg" class="source">Aidenvironment, 2005/Wikimedia Commons</a>, <a href="http://creativecommons.org/licenses/by-sa/4.0/" class="license">CC BY-SA</a></span></p> <h2>A climate change double whammy</h2> <p>In many parts of the world, including the tropics and Australia, expanding farmland is a major reason for cutting down forest. But given hotter temperatures also reduce the productivity of farms, conserving forests might prove a better strategy for food security and for the livelihoods of farmers.</p> <p>If forests must be removed, there may be ways to avoid the worst possible temperature increases. For example, we found that keeping at least 10% of forest cover helped reduce the associated warming by an average of 0.2℃.</p> <p>Similarly, temperatures did not increase as much when the area of forest loss was smaller. This means if deforestation occurs in smaller, discontinuous blocks rather than uniformly, then the temperature impacts will be less severe.</p> <p>To help share these findings, <a href="https://treeheat.azurewebsites.net">we’ve built a web mapping tool</a> that lets users explore the effects of different patterns and areas of forest loss on local temperatures in maritime South East Asia. It helps show why protecting forests in the tropics offers a climate change double whammy – lowering carbon dioxide emissions and local temperatures together.<!-- Below is The Conversation's page counter tag. Please DO NOT REMOVE. --><img style="border: none !important; box-shadow: none !important; margin: 0 !important; max-height: 1px !important; max-width: 1px !important; min-height: 1px !important; min-width: 1px !important; opacity: 0 !important; outline: none !important; padding: 0 !important; text-shadow: none !important;" src="https://counter.theconversation.com/content/163584/count.gif?distributor=republish-lightbox-basic" alt="The Conversation" width="1" height="1" /><!-- End of code. If you don't see any code above, please get new code from the Advanced tab after you click the republish button. The page counter does not collect any personal data. More info: https://theconversation.com/republishing-guidelines --></p> <p><span><a href="https://theconversation.com/profiles/sally-thompson-1223399">Sally Thompson</a>, Associate professor, <em><a href="https://theconversation.com/institutions/the-university-of-western-australia-1067">The University of Western Australia</a></em>; <a href="https://theconversation.com/profiles/debora-correa-1288935">Débora Corrêa</a>, Research fellow, <em><a href="https://theconversation.com/institutions/the-university-of-western-australia-1067">The University of Western Australia</a></em>; <a href="https://theconversation.com/profiles/john-duncan-1288934">John Duncan</a>, Research fellow, <em><a href="https://theconversation.com/institutions/the-university-of-western-australia-1067">The University of Western Australia</a></em>, and <a href="https://theconversation.com/profiles/octavia-crompton-1246306">Octavia Crompton</a>, Postdoctoral researcher, Pratt School of Engineering, <em><a href="https://theconversation.com/institutions/duke-university-1286">Duke University</a></em></span></p> <p>This article is republished from <a href="https://theconversation.com">The Conversation</a> under a Creative Commons license. Read the <a href="https://theconversation.com/deforestation-can-raise-local-temperatures-by-up-to-4-5-and-heat-untouched-areas-6km-away-163584">original article</a>.</p> <p><em>Image: Shutterstock</em></p>

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Global emissions to hit 36.8 billion tonnes – beating last year’s record high

<p>Global emissions for 2019 are predicted to hit 36.8 billion tonnes of carbon dioxide (CO₂), setting yet another all-time record. This disturbing result means emissions have grown by 62% since international climate negotiations began in 1990 to address the problem.</p> <p>The figures are contained in the Global Carbon Project, which today released its <a href="https://www.globalcarbonproject.org/carbonbudget/">14th Global Carbon Budget</a>.</p> <p>Digging into the numbers, however, reveals a silver lining. While overall carbon emissions continue to rise, the rate of growth is about two-thirds lower than in the previous two years.</p> <p>Driving this slower growth is an extraordinary decline in coal emissions, particularly in the United States and Europe, and growth in renewable energy globally.</p> <p>A less positive component of this emissions slowdown, however, is that a lower global economic growth has contributed to it. Most concerning yet is the very robust and stable upward trends in emissions from oil and natural gas.</p> <p><strong>Coal is king, but losing steam</strong></p> <p>The burning of coal continues to dominate CO₂ emissions and was responsible for 40% of all fossil fuel emissions in 2018, followed by oil (34%) and natural gas (20%). However, coal emissions reached their highest levels in 2012 and have remained slightly lower since then. Emissions have been declining at an annual average of 0.5% over the past five years to 2018.</p> <p>In 2019, we project a further decline in global coal CO₂ emissions of around 0.9%. This decline is due to large falls of 10% in both the US and the European Union, and weak growth in China (0.8%) and India (2%).</p> <p>The US has announced the closure of more than 500 coal-fired power plants over the past decade, while the UK’s electricity sector has gone from 40% coal-based power in 2012 to 5% in 2018.</p> <p>Whether coal emissions reached a true peak in 2012 or will creep back up will depend largely on the trajectory of coal use in China and India. Despite this uncertainty, the strong upward trend from the past has been broken and is unlikely to return.</p> <p><strong>Oil and natural gas grow unabated</strong></p> <p>CO₂ emissions from oil and natural gas in particular have grown robustly for decades and show no signs of slowing down. In fact, while emissions growth from oil has been fairly steady over the past decade at 1.4% a year, emissions from natural gas have grown almost twice as fast at 2.4% a year, and are estimated to further accelerate to 2.6% in 2019. Natural gas is the single largest contributor to this year’s increase in global CO₂ emissions.</p> <p>This uptick in natural gas consumption is driven by a range of factors. New, “unconventional” methods of extracting natural gas in the US have increased production. This boom is in part replacing coal for electricity generation.</p> <p>In Japan, natural gas is filling the void left by nuclear power after the Fukushima disaster. In most of the rest of the world, new natural gas capacity is primarily filling new energy demand.</p> <p>Oil emissions, on the other hand, are largely being driven by the rapidly growing transport sector. This is increasing across land, sea and air, but is dominated by road transport.</p> <p>Australia’s emissions have also seen significant reductions from coal sources over the past decade, while emissions from oil and natural gas have grown rapidly and are driving the country’s overall growth in fossil CO₂ emissions.</p> <p><strong>Emissions from deforestation</strong></p> <p>Preliminary estimates for 2019 show that global emissions from deforestation, fires and other land-use changes reached 6 billion tonnes of CO₂ – about 0.8 billion tonnes above 2018 levels. The additional emissions largely come from elevated fire and deforestation activity in the Amazon and Southeast Asia.</p> <p>The accelerated loss of forests in 2019 not only leads to higher emissions, but reduces the capacity of vegetation to act as a “sink” removing CO₂ from the atmosphere. This is deeply concerning, as the world’s oceans and plants absorb about half of all CO₂ emissions from human activities. They are one of our most effective buffers against even higher CO₂ concentrations in the atmosphere, and must be safeguarded. Not all sinks can be managed by people – the open ocean sink being an example – but land-based sinks can be actively protected by preventing deforestation and degradation, and further enhanced by ecosystem restoration and reforestation.</p> <p><em>Written by Pep Canadell, Corinne Le Quéré, Glen Peters, Pierre Friedlingstein, Robbie Andrew, Rob Jackson and Vanessa Haverd. Republished with permission of <a href="https://theconversation.com/global-emissions-to-hit-36-8-billion-tonnes-beating-last-years-record-high-128113">The Conversation.</a> </em></p>

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