The great scientific report on climate change blames humanity for the increase in extreme phenomena

It is no longer something more or less probable, but a fact. The latest major situation report of the IPCC, the panel of experts linked to the UN that has been laying the foundations on climate change for more than three decades, fulminates denialism and considers it “unequivocal” that humanity “has warmed the atmosphere, the ocean and the earth”, which has generated “widespread and rapid changes” on the planet. The previous edition of this study dates from 2013 and since then the evidence has multiplied, as have the scientific articles and analyses that show the consequences of a crisis that has already generated “unprecedented” changes in the climate in the last thousands of years and that in some cases will be “irreversible” for centuries or millennia. Among the direct consequences, in addition to the rise in average temperatures, are extreme weather events. These are events similar to heat waves or torrential rains that are being experienced in recent weeks in different parts of the globe and that have already increased in intensity and frequency due to human-generated warming, according to the report.

The study that has been made public this Monday is that of working group I of the sixth assessment report of the IPCC and 234 experts from 66 countries have participated in its preparation. Scientists have reviewed more than 14,000 articles and references published so far to make their synthesis on the physical effects that warming has already had and the possible scenarios depending on the greenhouse gases emitted by humanity in the coming decades.

These gases are mainly released when fossil fuels are burned to generate energy and are responsible for the overheating of the planet. Since the Industrial Revolution, emissions have not stopped growing, reaching unprecedented levels today. Two examples: the concentration in the atmosphere of carbon dioxide (CO₂) – the main one – is the highest reached in the last two million years; methane and nitrous oxide — the other two major precursors to warming — had not reached such high levels in the past 800,000 years. This has a clear consequence: the increase in global average temperature is already at 1.1 degrees above pre-industrial levels; and the rate of global warming is such that there is no precedent for a similar process in at least the last 2,000 years, the IPCC report notes.

The study warns that the increase in temperature will continue at least until the middle of this century no matter what. From 2050 things can get really complicated, because the level of warming will not be achieved to stay between 1.5 and 2 degrees “unless there are deep reductions in emissions of CO₂ and other greenhouse gases in the coming decades.” In the worst-case scenario, if action is not taken and emissions continue to grow at the same rate as before, the report estimates that by the end of this century an increase of 4.4 degrees would be reached, something that would also multiply the intensity and frequency of extreme events. Scientists remember that the last time a warming level above 2.5 degrees was reached was three million years ago, when the human being did not even exist.

The Paris Agreement, signed in 2015, set as its main objective to reduce emissions so that the increase in global temperature remained between those 1.5 and 2 degrees. And the IPCC reports also serve to notify countries’ leaders of what needs to be done to meet those commitments. Experts propose several emission scenarios during this century. In all of them, the 1.5-degree barrier is expected to be exceeded in the next 20 years due to the greenhouse gases that humanity has emitted so far and that remain in the atmosphere for decades. But Pep Canadell, director of the Global Carbon Project and one of the scientists responsible for the IPCC report, explains that the situation is not yet irreversible: in the most optimistic emissions scenario, it is still possible to achieve that the increase in temperature at the end of the century remains at 1.5 degrees although there may be a temporary exceedance of that threshold in the coming years.

To stay at 1.5 degrees, “rapid, sustained and large-scale” reductions are needed, as explained by Argentine climatologist Carolina Vera, one of the vice-presidents of IPCC working group I. Such emission reductions would take 20 to 30 years to have an impact on global temperatures. But the report notes that “the benefits to air quality would come quickly.” In addition to reducing emissions, to comply with Paris will need to resort to capturing the carbon dioxide that is already in the atmosphere through natural sinks, such as forests, or technological solutions, canadell adds. Of course, capture through natural sinks is limited, so it cannot be the main solution.

Paradigm shift

Since the first of these synthesis papers was published in 1990, evidence and studies on warming have been accumulating. But the IPCC’s final reports often use conservative language because they have to be approved by consensus among representatives of the 195 countries participating in climate negotiations at the UN. The scientific team of this sixth report presented its results to the countries at the end of July and during the last two weeks the final text of 42 pages presented on Monday has been negotiated and in which the debate on the influence of the human being on climate change is settled. In the drafting of the 2013 report, a minimal window was left open to doubt. But eight years later it closes definitively.

“The evidence for human influence on climate is already so overwhelming that there is no scientific doubt”

José Manuel Gutiérrez, director of the Institute of Physics of Cantabria (IFCA) and another of the coordinators of the report, explains it this way: “The IPCC uses a calibrated language that has to do with probabilities and with the available evidence. But human influence on climate no longer fits into any of those probability thresholds and is considered to be a proven fact that has no uncertainty. The evidence is already so overwhelming that there is no scientific doubt. This report uses such emphaticness not to continue with this debate; it is a fact and from there we will see how it affects and potential solutions”. Canadell considers that this is “a paradigm shift”: “We have thrown out the window the possibilities and the probabilities and it is concluded that it is a fact that the warming is due to humanity.”

Attribution of extreme events

The IPCC scientific team has been working on this report for three years. But the final stage has coincided with a concatenation of extreme weather events, such as the tremendous heat wave of late June in Canada, the floods in central Europe or China in July and the recent fires associated with heat in the Mediterranean basin. Precisely, another of the important novelties of the report is the one referring to these events. The IPCC states emphatically: “Human-induced climate change is already affecting many extreme weather and climate events in all regions of the world. Evidence of changes observed at extremes such as heat waves, heavy rainfall, droughts and tropical cyclones, and, in particular, their attribution to human influence has strengthened since AR5 [el informe de 2013].”

“It is virtually certain that extreme heat waves have become more frequent and intense in most terrestrial regions since the 1950s, while cold extremes (including cold waves) have become less frequent and less severe, with great confidence that human-induced climate change is the main driver of these changes.” A similar situation arises for “the frequency and intensity of intense rainfall events,” which have increased “since the 1950s across most of the earth’s surface” and of which “human-induced climate change is probably the main driver.”

Sergio Vicente-Serrano, a researcher at the Pyrenean Institute of Ecology, of the CSIC, and one of the authors of the chapter on extreme events, points out that the evidence on this link “is much more robust than in previous reports.” In 2013, for example, it was pointed to the possibility that these phenomena increased in virulence and frequency due to the energy that was accumulating in the atmosphere by warming. The big step that science has taken in recent years is the attribution of concrete extreme events to human-induced climate change, as happened with Canada’s heat wave. It has been achieved, Canadell explains, by technological advances — for example, with more powerful computers capable of handling much more data — and by the increase in these phenomena.

The report concludes that there is a “direct relationship” between rising average temperatures and the multiplication of warm extremes, heavy rainfall, agricultural and ecological droughts in some regions, in addition to the increase in intense tropical cyclones and the decrease in Arctic sea ice and the reduction of snow cover and permafrost. The text warns that, for every half degree of global warming, there are “clearly perceptible increases in the intensity and frequency of warm extremes, including heat waves (very likely) and heavy rainfall (high confidence level), as well as agricultural and ecological droughts in some regions (high confidence level).” And it warns that “there will be an increasing occurrence of some unprecedented extreme events in the observation record with warming,” even if the goal of 1.5 degrees is met.

Irreversible changes

The IPCC report recalls that many changes motivated by past emissions will already be “irreversible for centuries or millennia”, especially those affecting the oceans and ice sheets. Researcher Carolina Vera says these impacts “are going to continue for hundreds or thousands of years, but they can slow down if emissions are reduced.” It is expected, for example, that sea levels will continue to rise during this century. Between 1901 and 2018, the increase was about 20 centimeters. And, taking as a reference the level of the period between 1995 and 2014, by 2100 the rise could be 40 centimeters in the most optimistic emissions scenario; in the most pessimistic it would double, to exceed 80 centimeters. This will contribute to “more frequent and severe coastal flooding in low-lying areas and erosion” of the coast. “Extreme sea-level events that previously occurred once every 100 years could occur every year by the end of this century,” he said.
ica the IPCC.

“Extreme sea-level events that previously occurred once every 100 years could occur every year by the end of this century.”

Another of the critical points highlighted in the report is the Arctic, which will continue to warm more than twice as fast as the average on the planet. This would “further amplify the thawing of permafrost and the loss of seasonal snow cover, land ice and Arctic sea ice.” The scientists’ forecast is that the Arctic “will be virtually free of sea ice by September, at least once before 2050,” in all scenarios predicted in the report.

Reactions

“Today’s IPCC report is a code red for humanity,” said António Guterres, Secretary General of the UN, who said that “the viability of our societies” depends on the action of governments, companies and citizens to limit the increase in temperature to 1.5 degrees. “The alarms are deafening and the evidence is irrefutable: greenhouse gas emissions from burning fossil fuels and deforestation are choking our planet and putting billions of people at immediate risk. Global warming is affecting all regions of the Earth, and many of the changes are becoming irreversible,” said the Portuguese.

From the United States, President Joe Biden has also referred to this work of scientists: “We cannot wait to face the climate crisis. The signs are unmistakable. Science is undeniable. And the cost of inaction continues to rise,” the US leader said in a tweet.

For his part, Alok Sharma, president of the decisive World Climate Summit that will take place next November in Glasgow (COP26), has stressed that “the next decade is decisive”. “The science is clear, the impacts of the climate crisis can be seen around the world and if we don’t act now, we will continue to see how the worst effects impact lives, livelihoods and natural habitats.”

He also called for action by the Spanish Vice President and Minister for the Ecological Transition, Teresa Ribera, who has asked to “intensify efforts to adapt to climate change.” As he commented, “climate change is happening at an increasingly accelerated pace and scientific evidence pushes governments and the whole of world society to accelerate the pace of transformation of our development model and our economic system to face the great threat posed by climate change.”

Source: The Country