Expected ocean changes require planning many generations ahead, scientists say

Even if society is able to slow down all greenhouse gas emissions and reach “net zero” by the middle of the century, as envisioned by the countries of the world in the UN Paris Agreement, there is a slowdown. built into the climate system, mainly due to ocean thermal inertia. This means that slowly emerging changes, such as deep ocean warming and sea level rise, will continue long after.

Climate scientists argue in a new review article that this means determining climate action on multiple timescales. The article was recently published in Atmospheric and Oceanic Science Letters

The global ocean, which covers about 70 percent of the Earth’s surface, is slower to absorb and release heat than land. Its large mass and heat capacity also means that the ocean is much better able to store heat than air or land, and the ocean is therefore the main controlling component of the Earth’s climate.

This “thermal inertia of the ocean” offers both good news and bad news regarding climate change. It means the planet isn’t warming as fast as it would without an ocean. But it also means that even if we cut greenhouse gas emissions by 2050 to 2060, as enshrined in the United Nations’ Paris Agreement, the climate system will continue to change for quite some time after that.

The ocean will continue to warm as heat is transported down to deeper ocean waters, and the climate system will only restabilize when that deep ocean stops warming and the Earth reaches a balance between incoming and outgoing heat.

“This process means that although surface warming may stabilize at about 1.5-2 when global emissions reach net-zero emissions, the warming of the ocean below the surface will continue for at least hundreds of years, but we normally only talk about climate action on the scale of a few decades to the end of the century at the most,” said lead author, Prof. John Abraham, a mechanical researcher at the University of St. Thomas in Minnesota. “That has to change. “

Therefore, a system of scientific ocean monitoring needs to be developed with that timescale in mind. In addition to subsurface temperature and sea level, tracking ocean climate trends such as pH, sea ice, ocean surface heat flux, currents, salinity, carbon, requires long-term consistent and calibrated measurements. Compared to temperature, these essential climate variables are currently much less observed.

Observed trends in ocean heat content and ocean salinity over the past half century. Data from IAP Ocean Dataset (https://www.ocean.iap.ac.cn/). (Image by CHENG Lijing)

“Changes in the ocean will continue to impact extreme weather during these extended periods as well as sea level rise,” said Prof. CHENG Lijing of the Institute of Atmospheric Physics, Chinese Academy of Sciences. “And seawater infiltration into freshwater supplies can affect coastal food supplies, aquifers and local economies. Other effects linked to ocean warming and thus needing to be considered for the very long term include damaging storm surges. , coastal erosion, heat waves at sea, ocean acidification and depletion of oxygen in the sea.

“Clearly, this later group of measures will take much longer to implement, but also provide much longer-lasting benefits,” said climatologist Michael E Mann of Pennsylvania State University, another co-author of the paper. “Multiple scaling practices like these should be considered around the world.”

The researchers also suggest that societies should begin to consider ensuring they are resilient in the face of “high impact, low probability” events (an unlikely event that would have significant consequences if it did occur).

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