5th World Climate Report is no all-clear

IPCC: Climate change continues, ocean currently bears the brunt

Change in Earth's average surface temperature from 1901 to 2012 © IPCC AR5
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The warming is undoubted and will continue if nothing is done - this is the thrust of the much anticipated IPCC press conference on the 5th World Climate Review. Representatives of the authors and the IPCC emphasize that there is no reason to be all-clear, even though the atmosphere has been heating up less quickly than expected in recent years. Contrary to the last report from 2007, climate researchers therefore seem to be a little more optimistic about the future: they still believe that the two-degree climate protection goal can be achieved.

According to the latest World Climate Report in 2007, this is the fifth time that the combined expertise and data of climate researchers from all over the world are being evaluated to account for the planet's climate evolution. 209 lead authors and more than 600 other authors from 36 countries are involved in the first part of the 5th World Climate Report. It deals with the physical basis and thus the measured development of various climate parameters and the forecasts for the future trend. At today's press conference, the summary of the report, the so-called Summary for Policymakers (PDF), was presented. On September 30, then the entire first part of the report will be published. The other parts, which consider the climate impacts as well as possible measures, will not follow until next year.

Human influence even clearer

The main message of the IPCC is already clear at the press conference: "The warming is undoubted. Evidence of human influence has increased since the last climate report, "states the statements. The influence of humans is detectable in various components of the climate system - and it continues to increase. According to the new report, each of the last three decades has been warmer than any other decade since the beginning of industrialization. "In the Northern Hemisphere, the years 1983 to 2012 were probably the warmest 30-year period of the last 1, 400 years, " report the climate researchers.

Cover of the 5th World Climate Report of the IPCC © IPCC

As the measured data show, the snow and ice masses in the polar regions and mountains have also decreased further. The global sea level has also continued to rise - since 1901 now by a total of 19 centimeters. The increase in greenhouse gas emissions - and thus also their effect on the future climate - is also undiminished. Since the mid-1990s, CO2 emissions have increased by around half, and between 1995 and 2011, they have risen from 23 to 33 billion tonnes of CO2 per year.

"The continued emissions of greenhouse gases will result in further warming and changes in all components of the climate system, " explains Thomas Stocker, one of the two heads of the working group that produced the first part of the report. display

Two degree goal still within reach - if something is done

Specifically, the calculations showed that global warming by the end of the 21st century is likely to exceed 1.5 degrees in all but the most benign scenarios. If nothing or not much is done for climate protection, as is the case in three of the climate scenarios, the two-degree mark could also be exceeded, according to the climate researchers. "Limiting climate change will require substantial and sustained reductions in greenhouse gases, " stresses Stocker.

Sea level rise is projected to accelerate, according to IPCC researchers' forecasts: "It will increase at a faster rate than we have experienced over the past 40 years, " said Qin Dahe, the second director of Working Group 1. He said his colleagues predict that sea levels will rise by another 30 to 100 centimeters by 2100, depending on how much CO2 emissions are generated.

And there are hardly any deviations from the message of the last reports in terms of the tangible effects on climate: "As the planet warms, we expect rainy regions to receive more precipitation today, the dry ones, on the other hand, are less ", explains Stocker. Heat waves will become more frequent and longer lasting in the future.

The temperature of the earth's surface has risen more slowly since 1998. IPCC

Heating of the air has slowed down

One sensitive point, however, had led to speculation in advance: the fact that the Earth's atmosphere has warmed less in the past 15 years than the models predict. While the temperature increased by about 0.2 degrees per decade between 1950 and 1990, since 1998 it has only increased by about 0.05 degrees per decade. That brings the climate researchers in explanation N te. Because this slowdown in heating occurs, even though the concentration of the greenhouse gas CO2 in the atmosphere continues to rise.

For climate skeptics, this is a well-fed experience. After all, they doubt that humans and their CO2 emissions are to blame for climate change anyway. But the IPCC clearly contradicts that now. "Anyone who has hoped for the all-clear for the greenhouse effect, is disappointed, " commented Olaf Tschimpke, President of the environmental organization NABU. "Even though the warming of the land areas is at times slower, the effects of the unrestrained increase in CO2 in the atmosphere are more drastic than previously thought."

Ocean as a heat swallower?

One possible reason for the slower warming of the atmosphere is seen by the IPCC researchers in the oceans: the oceans have been heating up disproportionately in recent years. They could therefore have acted as a kind of heat sink for the air conditioning system. "The report notes with great certainty that the warming of the oceans has absorbed much of the increasing energy in the climate system, " explains Dahe. "This effect accounts for more than 90 percent of the energy that accumulated between 1971 and 2010."

For the planet's air envelope, this means a relief, but not for the oceans. Because they currently bear the brunt of climate change. After the already heated surface water, the deep sea could in future also show measurable temperature changes. The persistent increase in CO2 levels in the atmosphere also causes the acidification of seawater to continue to increase. For many lime and shell-forming animals such as corals, snails and shells this would be fatal.

(IPCC, 27.09.2013 - NPO)