The new UN climate change report documents the serious condition of the world’s glaciers
The United Nations agency for assessing climate change has just released the first part of its latest assessment report eight years after its last release.It details Working Group I of Intergovernmental Panel on Climate Change (IPCC) to the sixth assessment, based on the physical science of climate change. The other two components are scheduled to be released in 2022.
The IPCC prepares reports on the state of scientific knowledge about climate change and its effects, and creates mitigation and adaptation scenarios. Since 1990, a total of 6 major assessment reports have been issued, which are divided into three parts. work group organizational.
The report records the obvious changes in glaciers that have been almost universally observed in recent decades. The important statement pointed out that the global glacier retreat since the 1990s is likely to be driven by human influence, and the synchronous nature of almost all glacier retreats in the world has been unprecedented in the past 2000 years.
The cover of the first report of the IPCC’s sixth assessment. Credit: IPCC
Glaciers mainly appear in four of the twelve chapters. “Changes in the mass balance of glaciers will lead to changes in sea level, but also have a significant impact on the water supply of a considerable part of the population,” as described in Chapter 2, The changing state of the climate systemThe statement emphasized the importance of glaciers in the physical science of climate change.
Since IPCC 2019 Special report on the ocean and cryosphere (SROCC), new regional estimates and two new global glacier observation estimates have been released. Evidence shows that from 2010 to 2019, the quality of glacier loss was greater than in any other decade since the beginning of the observation record, which is said to be very reliable. The availability of high-precision data from individual glaciers and large-scale observations across mountainous areas have contributed to this major progress. Fifth Assessment (AR5) And SROCC.Since then, a new Learn It is estimated that the glacier will lose 18% of its mass under the RCP2.6 (low emission) scenario and 36% under the RCP8.5 (high emission) scenario.
In Chapter 9, Oceans, cryosphere, and sea level changes, Reported the detailed documentation of regional glacier observations. The glaciers in the Southern Andes, Central Europe, Alaska, and Iceland have the greatest loss in quality. The new reconstruction of the Patagonian Ice Sheet shows that the glaciers in the last century are retreating faster than at any time in the Holocene. Glaciers in the European Alps are now smaller than in the 16th century, glaciers in Norway are now smaller than at any time since the 9th century, and glaciers in the Canadian Arctic and Svalbard are smaller than in the past 4000 years.
Grinnell Glacier on Baffin Island in the Canadian Arctic is now smaller than at any time in the past 40,000 years. Credit Gregory Smith/Flickr.
The contribution of glaciers to changes in water supply is discussed in Chapter 8. Water cycle changesIn general, AR6 has collected a lot of evidence that in the short term, the runoff of the glacier recharge basin may increase, but then decrease as the mass is completely lost from the glacier.Under the medium emission scenario, glaciers in the Himalayas and Central Asia are expected to reach peak runoff between now and 2040, while peak runoff in low latitudes Andes The glacial river has passed. Both regions maintain large populations dependent on glacier water supply.
Another important topic is the contribution of glaciers to sea level rise. New modeling evidence estimates that from 1971 to 2018, ice loss from glaciers accounted for 22% of sea level rise. There is now a high level of confidence that melting ice sheets and glaciers were the main contributors to the global average sea level rise from 2006 to 2018. Nevertheless, it is still pointed out that the current generation of climate models does not fully consider many key components of the sea level budget, such as glaciers and ice sheets. The contribution of glaciers does not include the outer glaciers of Greenland and the Antarctic ice sheet. Increasing scientific attention is related to the large export glaciers that currently hinder most of the West Antarctic ice sheet because they are Antarctica’s largest contribution to sea level. AR6 reports with very high confidence that the Antarctic ice loss is mainly due to the acceleration, retreat and rapid thinning of these export glaciers, which is likely to be driven by the warming of the seawater located below and adjacent to the ice shelf.
Although both AR5 and SROCC believe that atmospheric warming is the (very) possible main driver of glacier retreat, a new Learn The conclusion of modelling 37 glaciers around the world is that if there is no anthropogenic climate change, the observed length changes will not occur. Using the same model, it is estimated that 85% of cumulative glacier mass loss since 1850 can be attributed to human influence.
Chimborazo volcano in Ecuador, the highest peak in the country. The top of the mountain is completely covered by glaciers, but new evidence finds that the peak runoff of the rivers supplied by these glaciers has now passed, threatening the area’s water resources. Credit: David Brossard/Flickr
Miriam Jackson, The glaciologist of ICIMOD and the lead author of SROCC, talked to GlacierHub about the importance of Assessment Report 6 (AR6) compared to previous IPCC publications. She explained: “People are saying things with greater confidence. We now know more and understand better.” Jackson explained that since AR5 and SROCC, the pace of scientific research and publication of research has accelerated. Although the AR6 plan was disrupted by the pandemic, Jackson stated that its release showed that “we can make huge changes and survive those changes.” Although the report shows that we are irreversibly committed to changing the world’s climate system, However, there are still opportunities to reduce emissions and control the temperature rise within the 1.5°C specified in the Paris Agreement, which will have a significant impact on the retreat of glaciers.
Jackson went on to explain that this latest information is very useful for COP26 to be held in Glasgow in November this year. The talks held at the event can rely on this document as evidence and explanation. “This is what you need to know, this is what is happening, this is very easy to get information,” Jackson commented.
Next year, report Climate change impacts, adaptation and vulnerability, and also Climate change mitigation Will be released as part of the IPCC’s sixth assessment.
Among the many details of AR6, there is one important point: the glacier strongly demonstrates the importance of reducing emissions immediately. The decisions made when countries gather at COP26 in just a few months will have huge consequences.
