This research digest reviews the most recent IPCC report about the impacts of climate change on the global ocean and Earth’s ice.

In the past year alone, the release of several large-scale global assessments has indicated in clear terms that the window to implement solutions is closing fast in order to limit global temperature rise and to safeguard biodiversity for a healthy planet. First, the Intergovernmental Panel for Climate Change (IPCC) released the “Special Report: Global Warming of 1.5°C” which demonstrated that while it is still technically feasible to avoid a 1.5˚C rise in temperature, annual emissions must be cut in half by 2030—thus providing about only a decade for major and immediate transformation.

Second, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services released a landmark report—often described as the equivalent of the “IPCC for biodiversity”—which estimated that one million species are at risk of extinction, due to threats from overfishing to development and deforestation. Third, the IPCC released a special report on climate change and land in August 2019 which found that a fundamental shift is required in global food production and land management in order to limit temperature rise to safe levels.

The most recent entrant to this compendium, the IPCC’s Special Report on the Ocean and Cryosphere in a Changing Climate summarizes decades of research from scientists worldwide, using 7,000 peer-reviewed studies, to assess how rising carbon emissions are affecting the global ocean, sea level, and ice formations. Before diving into the findings themselves, it is important to note that this report represents the first standalone assessment by the IPCC on the global ocean and the Earth’s ice. For a behind-the-scenes look at how the IPCC elevated the ocean to its own assessment, please see our interview with Dr. Jean-Pierre Gattuso, a lead author of the Special Report.

While there is a lot of material covered in the nearly 1,200-page report, here are a few of the main takeaways:

1) The ocean has borne the brunt of climate change impacts, and the effects are manifesting.

The IPCC’s Special Report states that it is “virtually certain” that the ocean has warmed unabated since 1970, absorbing more than 90 percent of excess heat energy since the 1970s. The report affirms that the rate of ocean warming has more than doubled since 1993. Without this buffer, the atmosphere would have heated up at a faster pace and scale than the average of one degree Celsius it has already warmed. This absorption of heat and emissions is causing significant impacts, from fueling cyclones, floods, and increased ice loss from Greenland and Antarctic ice sheets to causing large-scale coral bleaching events and extensive marine heatwaves.

In simple terms, climate change is changing the fundamental chemistry of the ocean and the effects will continue to exacerbate if greenhouse gas emissions continue to rise. By the end of 2100, the upper 6,500 feet of the ocean may absorb 5 to 7 times as much heat as it absorbed over the last 50 years (under a high emissions scenario). Hans-Otto Pörtner, a lead author of the report, put it this way: “The ocean is sending us so many warning signals that we need to get emissions under control. Ecosystems are changing, food webs are changing, fish stocks are changing, and this turmoil is affecting humans,” he told The New York Times.

2) One of the most prominent findings of the report is that climate change and its impacts—in particular sea level rise—are emerging faster than scientists previously thought.

The Special Report finds that global mean sea levels will most likely rise between 0.95 feet (0.29m) and 3.61 feet (1.1m) by the end of this century. This projection represents an upward revision, by about 10 percent, from the IPCC’s estimate in the Fifth Assessment Report released in 2014. The projections included in the Special Report therefore represent the highest sea level rise projections ever made by the IPCC. This upward revision in sea level rise was driven by both new observations of the climate system which have allowed for more or better data, as well as the accelerated rate of ice loss in particular from the Antarctic and Greenland ice sheets.

The Special Report finds that global mean sea levels will most likely rise between 0.95 feet (0.29m) and 3.61 feet (1.1m) by the end of this century. This projection represents an upward revision, by about 10 percent, from the IPCC’s estimate in the Fifth Assessment Report.

Source: IPCC, 2019: Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, M. Nicolai, A. Okem, J. Petzold, B. Rama, N. Weyer (eds.)]. In press.

3) The resulting impacts on natural ecosystems and human communities are not a distant notion; they are already being felt.

Marine ecosystems are feeling the impacts of these drivers of change, as observed with species migrating poleward to find cooler waters and massive die-offs of coral due to bleaching events. The impacts on ecosystem services have negative consequences for health and well-being, particularly for Indigenous peoples and local communities dependent on fisheries. The ability of the ocean to continue to provide ecosystem services, such as food security, will have global implications, whether an individual resides in Mumbai or Manhattan.

As it relates to warmer ocean temperatures and rising sea levels, these impacts will particularly imperil coastal regions of the world, even within current lifetimes. The Special Report states with high confidence that extreme sea level events that are historically rare (once per century in the recent past) are projected to occur frequently—at least once per year—in many locations by 2050. These projections hold for all RCP scenarios, with particular applicability to tropical regions.

A study by Climate Central released in October 2019—which was not assessed in the IPCC Special Report due to timing of publication—found that by 2050, rising sea levels could affect 3 times more people than previously estimated, with the greatest threat in coastal Asia. Developing projections of when and where sea level rise will be most significant can provide tangible guidance for coastal planning processes and infrastructure projects.

The Special Report states with high confidence that extreme sea level events that are historically rare (once per century in the recent past) are projected to occur frequently—at least once per year—in many locations by 2050.


Sea level rise increases the frequency of extreme flooding

Sea Level Rise HCEs

Note: ‘Future’ is used in this visualization because this change will occur at different times in different locations depending on the emissions scenario. Meeting Paris Agreement targets (RCP2.5 scenario) will result in 67% of locations assessed in the IPCC Special Report on the Ocean and Cryosphere experiencing this change by 2100. Business as usual (RCP8.5) will result in 90% of locations suffering what used to be 100-year floods on an annual basis. Source: IPCC, 2019: Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, M. Nicolai, A. Okem, J. Petzold, B. Rama, N. Weyer (eds.)]. In press.

4) Rapid emissions reductions can shield both marine ecosystems and human communities from the worst impacts of climate change. The most severe projections can be avoided if countries limit global warming to an increase of 2 degrees Celsius from preindustrial levels.

It is undoubtable that the most recent IPCC Special Report, along with other global assessments from the past year, have painted a grim picture for the ocean’s future if current rates of warming continue unabated. However, new literature—including the recent report from the High Level Panel for a Sustainable Ocean Economy—provide a pathway forward to stave off the worst impacts of climate change. The High Level Panel report outlines a model for leveraging ocean-based measures to provide up to 21 percent of emissions reductions required by 2050 to limit warming to 1.5 degrees Celsius. As the IPCC’s Special Report released in 2018 indicated, this window of opportunity is closing fast, with only about a decade to take decisive action.

“Our fate is probably somewhere in between” the best- and worst-case emissions scenarios laid out in the report, said Michael Oppenheimer, a lead author of the Special Report’s chapter on sea levels told The New York Times. “But if you think about the possibility of indefinite or even accelerating sea level rise for centuries to come, that bodes very poorly for coastal civilization.

As Drs. Jane Lubchenco and Steve Gaines suggested in a recent Science editorial, part of this paradigm change will require a new ocean narrative that transitions from seeing the ocean as “too big to fix” to “too big to ignore.” Science-based solutions provide a pathway forward for understanding how ocean-based actions can help shape our climate future.