The Earth’s climate system involves several slower processes that move heat between the atmosphere and the oceans. When the average heat in the oceans is the same as in the atmosphere, then the two are in equilibrium. The Long-term Equilibrium sea level rise (SLR) map in En-ROADS shows the estimated sea level rise that is expected to happen when the Earth’s heat is in balance.

Right now, though, the heat in the atmosphere and heat in the oceans are out of balance.

The amount of heat in the atmosphere has been steadily increasing as greenhouse gas emissions have risen. Greenhouse gases capture solar energy and increase air temperature. The heat in the atmosphere is transferred to the cooler ocean water, but this process is slow. Currently the gases are heating up the atmosphere faster than the ocean is absorbing heat.

If greenhouse gases emissions are net zero (emissions = removals), and concentrations of gases are constant, then the heat in the atmosphere will stop rising as quickly. The heat in the atmosphere will continue to be transferred into the oceans, increasing ocean temperatures. Eventually the heat in the atmosphere and the heat in the oceans will equalize. Again, this only occurs when the concentrations of greenhouse gases stop rising, which only occurs when net emissions are zero.

The process of transferring heat from the atmosphere into the oceans takes centuries to complete. The sooner that emissions reach net zero, the sooner the atmosphere and ocean can reach equilibrium with each other. The long-term equilibrium maps show what sea level could be 200-1000 years from now, after the heat transfer process finalizes.