ice bergs in the Arctic

Sea-level rising: the accelerating wave

Sea-level rising: the accelerating wave 1024 683 Mantle

Sea level rise is occurring faster than expected, impacting millions in the coming decades and potentially locking in irreversible changes for centuries to come, says the latest UN climate report. While there is uncertainty in the number of people impacted and how quickly these impacts will be felt, new science reveals that current projections for sea level rise may be too conservative.

Adaptation is a necessary response to rising seas, however according to a landmark report on adaptation, this response can only help mitigate problems in the short term. Even if we were to radically cut emissions, the world will see millions of people forced to migrate away from areas threatened by rising water levels. These reports make it clear that rapid decarbonization is required to avoid a highly disrupted future.

The oceans are warming and rising faster than thought, according to the September release of the United Nations’ Intergovernmental Panel on Climate Change’s (IPCC) special report on the Ocean and Cryosphere in a Changing Climate. In the report, the IPCC increased their projected end-of-century sea level rise (worst-case, business-usual) scenario to 61-110 centimetres, up from 52-98 centimetres found in the IPCC’s 2013 report, and up from 26-59 centimetres from its 2007 report.

Media reports mischaracterize IPCC’s 280 million error

Catching a lot of media attention from a leaked version of the IPCC’s special report was a figure citing a 2015 study estimating sea-level rise “associated with a 2°C warmer world could submerge the homeland of 280 million people by the end of this century”.

Despite media attention, the cited article looked at potentially displaced populations (based on 2010 population figures) from sea-level rise locked in this century, not occurring this century. Nevertheless, the media ran with this misquoted figure, and Mantle tweeted about it.

New studies: sea level rise predictions may be too conservative.

A month after the IPCC special oceans report was released, a new paper, published in Nature Communications, by Scott A. Kulp and Benjamin H. Strauss, used artificial intelligence to improve satellite projections for the number of people impacted by sea-level rise. Using ranges around the IPCC’s sea-level rise projections, the paper found that in a 2 °C world (emissions scenario RCP 4.5), approximately 360 million people will be threatened by annual flooding by the year 2100. More shockingly, by 2050 sea levels could threaten 150 million people, says the study.

Two months after the IPCC special report on oceans, another new multi-author study, also published in Nature Communications, revealed that over 125,000 years ago sea levels rose 10 metres above present levels with only one more degree of global average warming than our current level. This sea-level rise was driven by discharging land ice into the ocean from Antarctica, causing a dramatic three metres of rise per century. Several climate models have tried to capture the ice-cliff instability from land ice, but the “results are contentious,” said the authors of the paper in an Conversation news story. Nevertheless, those models found that Antarctica’s ice has the potential to contribute an extra metre of sea-level rise by 2100. The authors saw parallels between the past and our not-so-distant future, concluding that the melting polar ice sheets will likely affect future sea levels far more dramatically than anticipated to date. 

IPCC’s projections likely to continue to rise

It’s likely that in future reports the IPCC’s projections will increase as a result of the consensus nature of how these major reports are written. The IPCC, despite being attacked by climate skeptics and denialists as alarmists, are (and have been shown over time) to be conservative in their consensus view. When projections are agreed upon, more extreme scientific findings are thinned out, resulting in a unified voice that is not controversial, and is unlikely to be attacked by a well-organized climate denial community, says authors of a new book called Discerning Experts

The Antarctic ice could lead to sea-level rise of several metres “within a few centuries” and that observed changes “may be” the onset of an irreversible ice sheet instability, report the IPCC in their special report.

While there is still a great deal of uncertainty surrounding accurately projecting sea level rise, there is scientific evidence warning us that even with major global carbon reductions, current sea level rise will impact millions, and will perhaps be devastating for untold millions more.

Adapting to sea-level rise can help mitigate early losses

A recent landmark report by the Global Commission on Adaptation found that investing $1.8 trillion globally in five specific adaptation areas from 2020 to 2030 could generate $7.1 trillion in total avoided losses and related benefits. One of the five priority areas, directly related to sea-level rise, the commission, chaired by the UN Secretary General, recommended investing in was rehabilitating and planting mangroves. As sea-levels continue to rise and climate-related damage is exacerbated by more powerful storms, mangroves can help reduce the impact of storm surges. According to the report, these surges could otherwise destroy communities that have not invested in mangrove protection.

As temperatures rise and related impacts are increasingly felt, the commission says, “incremental adaptation will be insufficient and transformative approaches will be needed”, including situations where “coastal residents may need to systematically retreat.”

These warnings from our scientific community make it clear: if we don’t radically cut emissions, we doom millions of coastal dwellers to inundation, and lock in the eventual radical alteration of the inhabitable land on earth.