Global warming does not stop in a penny of a second. If people around the world stopped burning fossil fuels tomorrow, the stored heat would continue to warm the atmosphere.
Imagine how a radiator heats a house. The water is heated by a boiler and the hot water circulates through the pipes and radiators of the house. Radiators heat and warm the air in the room. Even after turning off the boiler, the already heated water continues to circulate through the system, heating the house. Radiators cool, but their stored heat continues to warm the air in the room.
This is called compromised heating. Likewise, the Earth has ways of storing and releasing heat.
Emerging research is refining scientists’ understanding of how the Earth’s global warming will affect the climate. While we once thought it would take 40 years or more for the planet’s surface air temperature to peak once humans stop heating the planet, research now suggests the temperature could peak in about 10 years.
But that doesn’t mean the planet will return to its pre-industrial climate or that we’ll avoid disruptive effects like rising sea levels.
I am a professor of climate science, and my research and teaching focus on the usefulness of climate knowledge to professionals such as city planners, public health professionals, and policy makers. With a new report on climate change mitigation due from the Intergovernmental Panel on Climate Change in early April, let’s take a look at the big picture.
How understanding of maximum warming has changed
Historically, early climate models only represented the atmosphere and were very simplified. Over the years, scientists have added oceans, land, ice caps, chemistry and biology.
Current models can more explicitly represent the behavior of greenhouse gases, especially carbon dioxide. This allows scientists to better separate warming due to carbon dioxide in the atmosphere from the role of heat stored in the ocean.
Thinking of our radiator analogy, increasing concentrations of greenhouse gases in the Earth’s atmosphere keep the boiler going, keeping energy near the surface and raising the temperature. Heat accumulates and stores, above all, in the oceans, which act as radiators. Heat is distributed around the world by weather and ocean currents.
The current understanding is that if all additional human-caused global warming were removed, a plausible outcome is that the Earth would reach a peak in planetary surface air temperature in more than 10 years than in 40. The previous estimate of 40+ has been widely used over the years, including by me.
It is important to note that this is only the peak, when the temperature begins to stabilize, not the start of a rapid cooling or climate change reversal.
I think there is enough uncertainty to warrant caution in overstating the importance of new research findings. The authors applied the concept of maximum warming to the air temperature at the surface of the planet. Global surface air temperature is, metaphorically, the temperature in the “room” and is not the best measure of climate change. The concept of instantly shutting off human-caused warming is also idealized and completely unrealistic; it would involve much more than just ending the use of fossil fuels, including widespread changes in agriculture, and would only help illustrate how certain parts of the climate behave.
Even if air temperatures peaked and stabilized, “committed ice melt”, “committed sea level rise” and many other terrestrial and biological trends would continue to evolve from the accumulated heat. Some of them could, in fact, cause a release of carbon dioxide and methane, especially from the Arctic and other high latitude deposits that are currently frozen.
For these and other reasons, it is important to consider how far in future studies like this.
the oceans of the future
The oceans will continue to store heat and exchange it with the atmosphere. Even if emissions cease, the excess heat that has accumulated in the ocean since pre-industrial times would influence the climate for another 100 years or more.
Because the ocean is dynamic, it has currents and will not simply release its excess heat into the atmosphere. There will be ups and downs as the temperature adjusts.
The oceans also influence the amount of carbon dioxide in the atmosphere because the oceans absorb and emit carbon dioxide. Paleoclimate studies show large changes in carbon dioxide and temperature in the past, with the oceans playing a major role.
The possibility that political intervention could have measurable impacts in 10 years instead of decades could motivate more aggressive efforts to remove carbon dioxide from the atmosphere. It would be very satisfying to see that policy interventions have present benefits rather than theoretical future benefits.
However, today countries are far from ending their use of fossil fuels. Instead, all evidence indicates that humanity will experience rapid global warming in the coming decades.
Our strongest finding is that the less carbon dioxide humans emit, the better off humanity is. Committed warming and human behavior underscore the need to accelerate efforts both to reduce greenhouse gas emissions and to adapt to this now warming planet, rather than just talking about all the must happen in the future.
This article was written by Richard B. (Ricky) Rood, Professor of Space and Climate Science and Engineering at the University of Michigan. It is republished from The Conversation under a Creative Commons license. Articles in English