The state of the climate in 2021 (2023)

From unprecedented wildfires in the US to the extraordinary heat of Siberia, the impacts of climate change were felt in every corner of the world in 2020. We have arrived at a "moment of truth", said United Nations Secretary-General Antonio Guterres, en suSpeech on the state of the planet in December. "Covid and the weather have brought us to a threshold."

BBC Future brings you our summary of where we stand on climate change as of early 2021, according to five crucial climate health measures.

1. CO2 levels

The amount of CO2 in the atmosphere reached record levels in 2020, reaching417 parts per millionin May. The last time CO2 levels exceeded 400 parts per million was aroundfour million years ago, during the Pliocene era, when global temperatures were 2 to 4 °C warmer and sea levels were 10 to 25 meters (33 to 82 feet) higher than they are now.

"We're seeing record levels every year," says Ralph Keeling, head of the CO2 program at the Scripps Institution of Oceanography, which has been monitoring CO2 concentrations from the Mauna Loa observatory in Hawaii since 1958. "We've seen record levels of new this year despite the Covid".

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The effect of the lockdowns on CO2 concentrations in the atmosphere wasso small that it registers as a "spot", barely distinguishable from the annual fluctuations of the carbon cycle, according to the World Meteorological Organization, and had a negligible impact on the general curve of increase in CO2 levels.

"We have put 100 ppm of CO2 into the atmosphere over the last 60 years," says Martin Siegert, co-director of the Grantham Institute for Climate Change and the Environment at Imperial College London. That is100 times fasterthan previous natural increases, such as those that occurred at the end of the last ice age, more than 10,000 years ago.

"If we continue at worst, by the end of this century CO2 levels will be 800 ppm. We haven't had that for 55 million years. There was no ice on the planet at that time and it was 12°C warmer. warm," he said. says Siegert.

CO2 emissions have increased rapidly since the 1970s (Credit: European Commission JRC EDGAR/Crippa et al. 2020/BBC)

2. Register the heat

The last decade was the hottest on record.. The year 2020 was more than 1.2°C warmer than the average year of the 19th century.In Europe, it was the warmest year on record, while globally 2020 tied with 2016 for the warmest..

Record temperatures, including 2016, often coincide with aEl Niño event (a large band of warm water that forms in the Pacific Ocean every few years), resulting in large-scale warming of ocean surface temperatures. But 2020 was unusual in that the world experienced a La Niña event (the reversal of El Niño, with the formation of a band of cooler water). In other words, without La Niña lowering global temperatures, 2020 would have been even hotter.

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• The rise of zero carbon shipping
• People exchanging planes for trains
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Unusually warm temperatures triggered theThe largest wildfires ever recorded in CaliforniamiColorado, It's in'black summer' of bushfires in eastern Australia. "The intensity of these fires and the death toll is really significant," says Siegert.

High temperature anomalies have become larger and more frequent in recent years on land, in the air and at sea (Credit: NOAA/BBC)

3. Arctic ice

Nowhere is this increased heat felt more than in the Arctic. In June 2020, the temperaturereached 38Cin eastern siberia, the hottest on record in the Arctic Circle. The heat wave accelerated the melting of sea ice in the East Siberian and Laptev seas and delayed the freezing of the Arctic by almost two months.

"You've definitely seen the impact of these warm temperatures," says Julienne Stroeve, a polar scientist at University College London. On the Eurasian side of the Arctic Circle, the ice didn't freeze until late October, which is unusually late. The summer of 2020 saw sea ice area at its second lowest on record, and sea ice extent (a larger measure, including ocean areas where at least 15% ice appears) also at its second lowest. low.

In addition to being a symptom of climate change, ice loss is also a determining factor. Bright white sea ice plays an important role in reflecting the Sun's heat back into space, a bit like a reflective jacket. But the arctic is warming uptwice as fastLike the rest of the world, and as less ice passes through during the hot summer months, we lose their reflective protection. Instead, large areas of murky water in the open absorb more heat, further fueling global warming.

Multiyear ice is also thicker and more reflective thanthe thin, dark seasonal ice that is increasingly taking its place. Between 1979 and 2018, the proportion of Arctic sea ice that is at least five years old fell from 30% to 2%, according to theIPCC.

"White ice reflects a lot of energy from the Sun and helps slow the rate of global warming," says Michael Meredith, a polar researcher with the British Antarctic Survey. "We are accelerating global warming by reducing the amount of sea ice in the Arctic."

Ice loss is thought to already be altering weather patterns around the world. In accordance withGrantham Institute, it is possible, though not conclusively proven, that Arctic conditions in 2018 triggered the "Beast from the East" winter storm in Europe in 2018 by disrupting the jet stream, a current of air high in the atmosphere.

"The temperature difference between the equator and the poles drives many of our large-scale weather systems, including the jet stream," says Stroeve. And because the Arctic is warming faster than lower latitudes, there is a weakening of the jet stream.

"Everything is interconnected. If one part of the climate system changes, the rest of the system will respond," says Stroeve.

Arctic sea ice has been declining rapidly since detailed records began in the 1970s, in a warming and melting feedback loop (Credit: NSIDC/BBC)

4. Freeze

Throughout the northern hemisphere, permafrost, ground that remains frozen year-round for two years or more, is warming rapidly. When the air temperature reached38C(100F) in Siberia in the summer of 2020, land temperatures in various parts of the Arctic Circle reacheda record 45C(113F), accelerating the thawing of the permafrost in the region. Both continuous (long, unbroken stretches of permafrost) and discontinuous (a more fragmented type) permafrost are in decline.

Permafrost contains a large amount of greenhouse gases, including CO2 and methane, which are released into the atmosphere during snowmelt. Soils in the permafrost region, which extends over about23 million square kilometers(8.9 million square miles) in Siberia, Greenland, Canada, and the Arctic, maintaintwice as much carbon as the atmosphere– almost 1,600 billion tons. Much of that carbon is stored as methane, a potent greenhouse gas with a global warming impact.84 times greater than CO2.

“The permafrost is doing us a huge favor by keeping that carbon locked out of the atmosphere,” Meredith says.

Melting permafrost also damages existing infrastructure and destroys the livelihoods of indigenous communities who depend on the frozen ground to move and hunt. It is believed to have contributed to thecollapse of a huge fuel tankin the Russian Arctic in May, which spilled 20,000 tons of diesel into a river.

As ground temperatures rise, even slightly, permafrost around the world begins to thaw, releasing greenhouse gases (Credit: Biskaborn et al. 2019/Nature Communications/BBC)

5. Forests

Since 1990 the world has lost178 million hectares of forest(690,000 square miles) – an area the size of Libya. Over the past three decades, the rate of deforestation has slowed, but experts say it's not fast enough, given the vital role forests play in curbing global warming. In 2015-20, the annual rate of deforestation was10 million hectares(39,000 square miles, or about the size of Iceland), compared with 12 million hectares (46,000 square miles) in the previous five years.

"Globally, forest areas continue to decline," says Bonnie Waring, Senior Lecturer at the Grantham Institute, noting that there are large regional differences. “We are losing a lot of tropical forests in South America and Africa [and] restoring temperate forests through tree planting or natural regeneration in Europe and Asia.”

Brazil, Democratic Republic of Congo and IndonesiaThey are the countries that lose forest cover the fastest. In 2020, deforestation in the Amazon rainforest reached ahigh 12 years.

An estimate45% of all carbon on earthit is stored in trees and on the forest floor. “Soils globally contain more carbon than all plants and the atmosphere combined,” says Waring. When forests are cleared or burned, the soil is disturbed and carbon dioxide is released.

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• The revolutionary plan to save the Congo Basin
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The World Economic Forum launched a campaign this year to plant a trillion trees to soak up carbon. While planting trees can help cancel out the CO2 emissions of the last 10 years, it can't solve the climate crisis on its own, according to Waring.

“Protecting existing forests is even more important than planting new ones. Every time an ecosystem is disturbed, carbon is lost,” he says.

Allowing forests to grow naturally and reforesting large areas of land, a process known as natural regeneration, is the most cost-effective and productive way to capture CO2 and increase overall biodiversity, according to Waring.

Global deforestation rates are slowing overall, but in some of the world's most pristine forests it is still rapid (Credit: FAO/BBC)

In addition to showing how much the climate has already changed, these five climate indicators also point the way toward solutions that can reduce global warming to safer levels by the end of the century.

As Guterres noted in his State of the Planet speech in December: "Let's be clear: human activities are at the root of our descent into chaos. But that means human action can help solve it."

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With data investigation by Miriam Quick.

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