Despite the hiatus, global warming is unequivocal

The UN Intergovernmental Panel on Climate Change concluded on Friday that it is now more certain than ever before that human-caused climate change is real, and greenhouse gas emissions are causing changes to the planet that could possibly trigger dangerous consequences by the turn of the century.

These conclusions came as part of the Summary for Policymakers (SPM) on the physical science of climate change — a report prepared by scientists on the panel and finally negotiated by governments to sum up the latest scientific research on the issue and meant to guide climate negotiations. The report was formally adopted in Stockholm on Friday. The last such report was brought out in 2007.

The panel concluded that the “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.”

The Hindu had reported on the final draft of the SPM, which had for the first time acknowledged a hiatus in rising atmospheric temperatures between 1998 and 2012. The approved report on Friday accepted the controversial hiatus but diluted the significance of the episode noting natural variations in the climate could cause such aberrations and that while studying climate change, longer periods were more reflective of the trends.

The panel concluded: “Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850.”

The report also concluded that the greatest alteration to climate is caused by the cumulative carbon dioxide emissions, as compared to other short-lived, climate-forcing gases.

In the relative short-run, global mean surface temperatures are likely to increase in the range of 0.3-0.7 degree Celsius over the 1986-2005 average. Over the long run, between 2081 and 2100, the temperatures are likely to rise anywhere between 0.3-4.8 degree Celsius depending upon how much more emissions are released.

Krishna Kumar Kanikicharla, one of the lead authors of the report, told The Hindu, “The report presents different emission pathways and the change in temperatures those emission levels are likely to cause.”

The report indicated that unless strong emission reduction measures are taken in coming years the likelihood of temperature increase as compared to industrial-age levels remaining below 2 degree Celsius are less than likely. The 2 degree Celsius increase is taken as a tipping point beyond which scientists believe dangerous levels of climate change would be unleashed.

The report said that limiting the warming to less than 2 degree Celsius with a 66% confidence level requires that cumulative carbon dioxide emissions are restricted to 840 giga tonnes of carbon (GtC). The cumulative carbon dioxide emissions had touched 545 GtC by 2011.

Kanikicharla also said: “My takeaway from the report is that except for the hiatus, all other indicators of climate change, such as seal level rise, arctic ice cover are showing a monotonous trend of things getting worse with rise in emissions. These indicators are showing no pause.”

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Printable version | Oct 15, 2021 9:46:01 PM | https://www.thehindu.com/sci-tech/energy-and-environment/despite-the-hiatus-global-warming-is-unequivocal/article5175117.ece

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