The United Nations is preparing to release the most confident and comprehensive assessment of global warming to date, including detailed estimates of how the continued greenhouse gas emissions in the next few years will increase the earth’s sea level and promote extreme weather. The Intergovernmental Panel on Climate Change (IPCC) report is compiled by more than 200 scientists and approved by government representatives from 195 countries/regions. There is no doubt that human beings are changing the way the earth works-if there is a problem with the government, the situation Will get worse.The climate researchers interviewed said not to take drastic action nature.
Many people hope that this report covering the latest developments in climate science will inspire action at the United Nations Climate Summit in Glasgow, UK in November this year, when world leaders will make new commitments to curb greenhouse gas emissions. Scientists say that under current policies, governments will not be able to achieve their goal of limiting global warming to 1.5-2°C higher than pre-industrial levels set in the 2015 Paris Climate Agreement.
Corinne Le Quéré, a climate scientist at the University of East Anglia in Norwich, UK, said: “This report will clearly state the current state of science and throw the ball back into the government’s camp to take action.”
This is the first of the three reports of the IPCC’s sixth major climate assessment since 1990: the second is on climate impact and adaptation, and the third is on mitigation efforts, which will be released next year. The first report is expected to be released next week, nature Preview what the researchers say are some of the most important advances in climate science since the last IPCC assessment eight years ago.
High confidence, hot sale
After decades of research, climate scientists have no doubt that greenhouse gas emissions will cause global temperatures to rise. Since the pre-industrial era, the concentration of these gases has increased by about 50%, and the earth has warmed by more than 1°C (see “Warm World”). It is estimated that unless governments take more measures to curb these emissions, the world will heat up by nearly 3°C.
As climate science advances, researchers are becoming more and more confident in such predictions-the IPCC report will emphasize this point. One way scientists evaluate climate predictions is through an indicator called climate sensitivity. This is a measure if the carbon dioxide (CO2) The level has doubled compared with the pre-industrial level. Despite advances in understanding and computing power, estimates of climate sensitivity have remained at around 1.5-4.5 °C since the 1970s. Recent efforts to narrow the scope have greatly enhanced scientists’ trust in the predictions of the rate of world warming in the coming decades.
For example, in a study published in July 2020, a group of researchers challenged climate models with a variety of evidence, including contemporary climate records and evidence from ancient climates. They determined a possible climate sensitivity of 2.6–3.9 °C.
“This sounds a bit esoteric, but if the IPCC narrows the range of climate sensitivity, it will actually be a big deal,” said Zeke Hausfather, a climate scientist at the Breakthrough Institute in Oakland, California, co-author of the study. . Reducing the scope will help constrain the model and improve future predictions.
But Hausfather was quick to point out that many of the latest climate models—including models from large modeling centers in the United States and the United Kingdom—predict warming even much higher than previous estimates of climate sensitivity. Of the approximately 40 models running climate sensitivity tests, approximately one-third predicted that if carbon dioxide emissions exceed 4.5°C2 The level has doubled, which puzzles scientists, who believe that this extreme level of warming is unreliable given other evidence.
Scientists are still investigating why these models run so hot, but some studies suggest that part of the answer may be the use of complex new representations of cloud microphysics and tiny particles called aerosols in the atmosphere. For example, early models were characterized by unrealistic clouds made up of too much ice, which would turn into water as the world warmed. This creates a cooling effect because the water-based cloud reflects more solar energy back into space. The latest model starts with a more realistic cloud, with more water in it, which reduces the cooling effect over time.
But this is only part of the larger equation that climate scientists are still working on, says Gavin Schmidt, head of the modeling team at NASA’s Goddard Institute for Space Research in New York City. Schmidt said that when calculating indicators such as climate sensitivity, some thermally operating models may need to reduce the weight. But he added that they can still provide useful predictions for climate variables such as precipitation patterns.
Schmidt said that when interpreting the latest climate predictions, the IPCC should recognize that scientists have only just begun to study these issues in depth.
When the IPCC was convened, the world got a glimpse of how the earth’s sea level will rise Release 2019 special reportExperts say that the science it proposes will undoubtedly be included in next week’s release. It points out that by 2100, the global average sea level will rise by 0.3 meters to 1.1 meters, depending on greenhouse gas emissions. This is only slightly higher than previous forecasts, but the report also cited recent studies analyzing the opinions of experts in the field, who claimed that the possibility of a 2 meter rise cannot be ruled out. Such extreme changes could displace tens of millions of people in low-lying areas.
Determining sea level rise is difficult, because it depends on the complex question of whether the ice sheets in Greenland and Antarctica will collapse—if so, how quickly they collapse. However, since the last major climate assessment of the IPCC in 2013, scientists have made significant progress in understanding how the rising tide affects communities on a local and regional rather than global scale. This is important because different cities, countries, and regions will experience sea level rise in very different ways, as Michael Oppenheimer, a climate scientist at Princeton University in New Jersey, and the author of the IPCC special report, said.
For example, the ice sheets of Greenland and Antarctica are very large, and they produce gravitational effects that cause the surrounding ocean to expand. When some of the ice melts, the local expansion subsides and the water redistributes to other places, such as the northeastern United States-causing sea levels there to rise.
“This is the first time that the IPCC has conducted a comprehensive analysis of all these local and regional impacts,” Oppenheimer said. He said this information is important because even a seemingly small rise in local sea levels can have a major impact-especially on flooding during storms. Oppenheimer added that in many parts of the world, by the end of this century, the once-in-a-hundred-year flood will be an annual event, even in the most optimistic climate scenarios.
Next week’s IPCC report follows the epic flood in Germany in July and the heat wave in June that swept across the Pacific Northwest and western Canada, where the town of Litton recorded a record 49.6° before wildfires almost razed it to the ground. The temperature of C reaches the ground. Soon after, Climate scientist assessment The heat wave and the conclusion that global warming is almost certainly a driving factor, since the end of the 19th century, the probability of such an event has increased 150 times.
Just ten years ago, when asked about the connection between global warming and any single extreme climate event, scientists often objected, saying that as the climate warms, we should expect more such events. But Sonia Seneviratne, a climate scientist at the Swiss Federal Institute of Technology in Zurich, said that the science of climate attribution has made great strides in recent years. Therefore, even though the recent heat wave analysis will not be included in the new IPCC report because it was not released in time, there is still a large amount of research on extreme weather available for IPCC evaluation, Seneviratne said.
Two things have driven this change.First of all, climate scientists Developed improved models and statistical methods Used to determine the probability of any given climate event, regardless of whether there is a human-induced climate change. But just as important, Senviratne said, climate change itself is advancing, and recent research shows that more and more extreme weather events are now appearing on top of the noise of natural changes.
Or, in Le Quéré’s words, we can now see the effects of global warming “with our own eyes.”
This article is reproduced with authorization and has been First published August 5, 2021.