Climate change update

A landmark climate change report signed by 234 scientists from more than 60 countries concluded that the world could temporarily reach 1.5 degrees Celsius within 20 years, even under the best conditions of drastically reduced greenhouse gas emissions The warming up.

Scientists say that even if emissions decrease rapidly, temperatures will continue to rise, “at least” until 2050, and lead to further extreme weather events.

They stated that without “immediate, rapid and large-scale reduction” of emissions, it will be “out of reach” to control global warming by 2100 at 1.5 degrees Celsius or even 2 degrees Celsius higher than pre-industrial levels.

The latest analysis of the science of global warming by the United Nations Intergovernmental Panel on Climate Change is the sixth such report and the first since 2013. The summary was reviewed by representatives from 195 countries and will form the basis for negotiations at the November Global Summit.

The harshly worded report stated that the evidence of man-made climate warming was “unambiguous” and its effects are being felt around the world.

The lead author of the report, Ed Hawkins, said: “We have seen the impact, and with each point of warming, the situation will only get worse.” Work for three years.

Main findings of IPCC

  • global warming: 0.95 to 1.2C, since the late 1800s.For at least the past 2000 years, the surface temperature has risen faster since 1970 than in any other 50-year period

  • Global warming under very low emission scenarios: Increase the temperature by 1.5C by 2040 and 1.6C by 2060

  • Global warming under high emission scenarios: Carbon emissions have tripled, and the temperature rise may reach 1.9C by 2040, 3C by 2060, and 5.7C by 2100

  • Sea level under very low emission scenario: Compared with the level in 1900, an increase of about 0.35m by 2050 and an increase of about 0.5m by 2100

  • Sea level under high emission scenarios: Increase by about 1 million by 2100

  • Sea level when the ice sheet is completely melted: Ascent about 65m

  • Arctic: There may be “almost no sea ice” at least once in September before 2050

The 1.5C threshold has become a rallying point because the earth is expected to heat up by 1.2C in 2020, with an average temperature of 1.1C over the past ten years. G7 countries pledged in May Limit warming To 1.5C, this is a shift from the headline goal of the 2015 Paris Agreement to keep the temperature “well below 2C”.

Pierce Foster, one of the lead authors of the report, said: “If the world can significantly reduce emissions in the 2020s and achieve net zero carbon emissions by 2050, the temperature rise can still be limited to 1.5C.”

John Kerry, the President’s special envoy for climate change, said the survey results emphasized the “urgency of this moment”. United Nations Secretary-General António Guterres described these conclusions as “the red code of mankind.”

According to several people involved in the discussion, in virtual negotiations with scientists, Saudi Arabia opposed some of the wording of the abstract. The representative of this oil-dependent kingdom tried to replace “carbon emissions” with “greenhouse gas emissions”. But “science has the upper hand,” one person present said.

Researchers say that overall warming is “led by past and future carbon emissions,” but it is also necessary to urgently reduce methane, the shorter-lived but more potent pollutant.

Methane released through agriculture and poorly managed natural gas production absorbs more heat than carbon dioxide.

The line chart shows the estimated annual methane emissions under the five theoretical paths as of 2100

In the best case that scientists have simulated-more carbon removed from the atmosphere than added to the atmosphere, shortly after 2050-the temperature increase may reach 1.5 degrees Celsius by 2040 and 1.6 degrees Celsius by 2060 Degrees Celsius. However, by 2100, the temperature may drop to 1.4C.

A similar path modeled by the IPCC in 2018 1.5C Special Report It is said that warming may exceed this level in 2035. Except for some methodological differences, “[the science] It hasn’t really changed” because of that estimate, Foster said. The timetable for reaching 1.5C under comparable emission paths in the two reports is “almost the same”.

Researchers estimate that in a less ambitious scenario—the world reaches net zero carbon emissions around 2075 and net negative emissions soon thereafter—warming may be limited to 1.8C by 2100, but it may Will exceed 2C. The report’s other lead author, Joeri Rogelj (Joeri Rogelj), stated that the world is currently off this path.

According to the report, in a “very high” emission scenario—carbon emissions are three times what they are today—the warming may reach 5.7C by 2100.

Rogelj said the new evidence supports the view that “if we reduce emissions to net zero and keep them at net zero, warming will stabilize.” He added that going beyond net zero by removing large amounts of carbon from the atmosphere “may be able to reduce warming.”

The report warns that decarbonization technologies are “not ready” to function at the required scale, and that most technologies “have undesirable side effects.”

It is estimated that if the possibility of limiting the temperature rise to 1.5C is as high as 83%, then the world can only add 300 gigatons of carbon to the atmosphere.Global energy related Carbon emissions in 2020 are 32 gigatons, According to the International Energy Agency.

Researchers say that even in the case of global warming of 1.5 degrees Celsius, the number of “unprecedented” weather events will increase. Disasters such as floods and heat waves are expected to become more frequent and severe.

The report said that although warming may still be limited, some changes that have occurred over the centuries or thousands of years are “irreversible”, such as rising sea levels.

The small multi-column chart shows the estimated contribution of different emissions to the increase in global surface temperature, and carbon dioxide emissions dominate under five theoretical pathways

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