Science Behind Climate Change: The Ocean & Cryosphere

By: Meera Nayak, J.D., University of Denver Sturm College of Law

“The ambitious climate policies and emissions reductions required to deliver the Paris Agreement will also protect the ocean and cryosphere – and ultimately sustain all life on Earth.” - Debra Roberts, Co-Chair of IPCC Working Group II

“The open sea, the Arctic, the Antarctic and the high mountains may seem far away to many people...[b]ut we depend on them and are influenced by them directly and indirectly in many ways – for weather and climate, for food and water, for energy, trade, transport, recreation and tourism, for health and wellbeing, for culture and identity.” - Hoesung Lee, Chair of the IPCC

From the Global Climate Strike to Fridays for Future to Extinction Rebellion, protests and movements have erupted around the world. Demands for government action to reduce greenhouse gas emissions and declarations of a climate emergency ring out from London, Germany, Australia, the Netherlands, New York, Jakarta, Guadalajara, Kampala, Amman, Québec, and other places. As of October 11, 2019, 1,119 jurisdictions in 20 countries have declared a climate emergency. What is the latest science behind climate change that forms the basis for these demands and declarations?

At its 51st session (September 20 – 23, 2019), the Intergovernmental Panel on Climate Change (IPCC) approved and accepted the Special Report on the Ocean and Cryosphere in a Changing Climate (Special Report). The IPCC “is the United Nations body for assessing the science related to climate change” and 104 leading scientists prepared the report. This post will outline the most dramatic findings of the report.

The focus of the Special Report is on the ocean and the cryosphere. The ocean contains “97% of the Earth’s water” and the cryosphere is the “frozen components of the Earth system.” According to the report, there is a projected irreversible response by the ocean and the cryosphere to “past and current human-induced greenhouse gas emissions and ongoing global warming.” Millions of people are exposed to changes in the ocean and cryosphere, particularly those communities in “coastal environments, small islands...polar areas and high mountains.” These communities are exposed to “sea level rise, extreme sea level and shrinking cryosphere,” while other communities further from the coast are still exposed to “extreme weather events.”

Observed Changes and Impacts

The report states “it is virtually certain [99-100% probability] that the global ocean has warmed unabated since 1970 and has taken up more than 90% of the excess heat in the climate system” and that “by absorbing more CO2, the ocean has undergone increasing surface acidification.” The report highlights with very high confidence (highest level of confidence) the following impacts: the “widespread shrinking of the cryosphere, with mass loss from ice sheets and glaciers”; “reductions in Artic sea ice extent and thickness”; “increased permafrost temperature”; “very likely” doubling of marine heatwaves in frequency since 1982 and current increase in intensity; and global mean sea level rise “with acceleration in recent decades due to increasing rates of ice loss from the Greenland and Antarctic ice sheets.”

Projected Changes and Risks

The report states that it is virtually certain that “over the 21st century, the ocean is projected to transition to unprecedented conditions with increased temperatures” and “further acidification.” With very high confidence, the report states that “marine heatwaves...are projected to become more frequent” and “warm water corals,” which are already at high risk, “are projected to transition to very high risk even if global warming is limited to 1.5°C.” According to the report, it is very likely that “the Atlantic Meridional Overturning Circulation...is projected to weaken” and that “the ocean is projected to transition to unprecedented conditions with...greater upper ocean stratification.” Overall, the “rates and magnitudes of these changes will be smaller under scenarios with low greenhouse gas emissions.”

Recommendations

To address the aforementioned changes, impacts, and risks, the report recommends “urgent and ambitious” emissions reductions and adaptation actions. The report also emphasized the need for “cooperation and coordination” among governments. Finally, the report called for improved “climate literacy” and capacity-building. These measures have the potential to enable climate resilience and sustainable development in turn by addressing climate-related changes in the ocean and cryosphere.