The IPCC delivers its starkest warning about the world�s climate

AT A KEY moment, the Jaws film features police chief Martin Brody who, after knowing that shark attacks were possible, actually witnesses one. Stephen Spielberg, the director, highlights Brody's transformative shock by using a clever camera technique called a "dolly zoom". Nothing actually moves on the screen. Brody's guilty look seems to be rushing towards the camera, taking up more of the frame. His surroundings are also revealed more clearly, and not being displaced. The Intergovernmental Panel on Climate Change released the first part (AR6) of its sixth assessment report on August 9. It shows the unnerving spectacle of the impossible becoming real. It is now more obvious than ever that there is a risk of continuing warming. However, the details of the already occurring changes can be seen in a wider context. The coming dread is more evident than in the IPCC's last major assessment, AR5, published in 2013. Since then, the Earth has warmed by approximately 1.1C (2F) more than it was in 1921. Even if countries around the world drastically cut greenhouse-gas emissions (they aren't yet on any consistent downward trend), the IPCC found that temperatures will be 1.5C higher by 2050 than they were in 19 century, if not earlier. This breaks down the most ambitious goal of limiting climate change, which the world agreed to in 2015's Paris agreement. The IPCC was proud to endorse the idea that global warming is closely related to cumulative greenhouse-gas emissions. This allows for the calculation of carbon budgets associated with different temperatures. This budgeting process has been repeated for AR6. With a 50/50 chance of staying below 1.5C, the budget allows for just 500bn tonnes more carbon dioxide to be released. This is roughly 15 years worth of industrial emissions at current levels (emissions due to deforestation are worse). To achieve this level of emissions, the entire world would need to be net-zero by 2050. The report lays out the increasing difficulty in meeting this central challenge. It also shows how much science can now be said about the nature and extent of the changes under way, providing a more complete context. It is more assertive than previous reports in its ability to attribute changes and specific events to climate, describe the distribution of these effects all over the Earth, and assess the extent to which weather is being pushed into new extremes. These conclusions are based on multiple lines of evidence. Not just computer models output, but also improved physical understanding of various processes and observations of how the world has changed over time. These changes are now affecting all inhabited regions of the world, and human influence is contributing to many observed climate extremes. The IPCCs assessments are a huge commitment of time and effort by researchers from around the globe. The assessments are composed of three distinct working groups. One examines the state of climate science, while the second evaluates research on adaptation and vulnerability, and the third considers the potential for mitigation. The releases of reports from different working groups are usually spread over several years. This is the case with the Working Group Is report about the physical science. The summary for policymakers is a crucial component of the document. It is also, in some ways, a summary written by policymakers. The five-day long plenary process concluded on August 6th. The governments that make up the IPCC analyzed a draft summary prepared for them by scientists to create a text which could be agreed upon by all. This process has been fraught with difficulties in the past, with some governments refusing to accept that scientists did not express their concerns as clearly as they wanted. The governments' editing rights were primarily used to include language that was desired by different parties in order to subtly support their negotiating positions at COP26, which is the UN climate conference, which will be held in Glasgow in November. This simple passage is likely to reflect the new level of confidence that the scientists have shown in the conclusions of their report. In the summary, the authors who express high confidence far outnumber those with medium confidence. The previous report was based on level pegging. High confidence areas that were lacking in the previous report include the belief that human influence has increased the frequency and intensity of concurrent heatwaves in the world; that heavy rain and flooding will become more common in Asia and Africa at 1.5C; that certain mid-latitude regions such as south, central, and eastern Europe are expected to experience the greatest increase in temperature on the hottest days at approximately 1.5 to 2x the rate of global heating; The reports estimate of equilibrium climate sensitivity, the amount of warming that can be expected due to a doubling in carbon-dioxide levels, is another important indicator of confidence. This number was between 2 and 4C in 2007's AR4; however, the uncertainty has increased slightly in 2013's AR5, expanding the range to 1.5-4.5C (range 3) It has been reduced to half: AR6 now puts the sensitivity at 2.5-4C with a best estimate being 3C. Better science is a part of the reason for higher levels of confidence, which is always a good thing. Part of the higher confidence is due to bitter experience, which isn't. The report emphasizes that the world is experiencing climate change now, and not just watching it happen. The multiple evidence points that go beyond theory and modelling to observe what has been happening in the past decade are just a few examples. Good news is available for those who view the world as half-full. According to the report, large-scale carbon dioxide removal from the atmosphere could be an effective way to reduce temperatures. This is a good thing, as policymakers are increasingly dependent on large-scale carbon-dioxide removal as a way to reconcile the modest near-term reductions they actually deliver with their long-term goals. The IPCC would have ruled out large-scale carbon dioxide removal as a viable option. This would have scuttled the idea of aiming for net-zero emission, which is a state in which as much greenhouse gas is removed from the atmosphere as it is added. However, the report notes that such removals could have consequences for other things than temperature. This includes food production and water availability and quality. The report also highlights methane as the second-most important greenhouse gas that is being emitted in large quantities by humans. Like the atmospheric carbon dioxide level, atmospheric methane is higher than ever before in human history. Atmospheric methane, unlike carbon dioxide is very short-lived. Methane emissions can be cut much more quickly than carbon dioxide, which means that they will pay off in terms averted warming. The world must make it a priority to reduce methane emissions from both industry and agriculture if they want to limit global warming to below 1.5C. As the report points out, this is particularly important because of the effects of another pollutant--sulphates, which are given off mostly by coal plants and by heavy fuel oils. Sulphates, unlike greenhouse gases, reduce global warming by reflecting sunlight back into space. According to the IPCC, they keep the world around 0.5C cooler than normal. Without sulphates, there would be a 50/50 chance that the world would get 1.5C or more warm than it did in the 19th century. However, sulphates can also be deadly. They have been a major contributor to particulate pollution over the past decade that has claimed the lives of tens and millions. They have been increasingly removed from fuels and smoke stacks as a result. According to the IPCC, net warming is a result of all the emission scenarios that it examined. This is why it recommends that methane emissions be reduced rapidly and continuously. However, if methane goals are not increased, increasing temperatures will continue to rise. Jaws' coup de cinéma by Mr Spielberg marks the moment that the chief realizes that there is no way to prevent calamity; his inaction has made a covert threat a bloody-in-the water reality. This process of climate change has been ongoing for about a decade. However, in this summer of broken temperature records, terrifying fires, and floods, an IPCC Report in which models of climate changes are supported up with observations should provide a similar punctuation and a call for Glasgow's COP26. Register for The Climate Issue, our twice-weekly newsletter, to get more coverage on climate change. Or visit our climate-change hub.

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