Even After Emissions Are Reduced, We'll Still Have to Contend With 'Committed Warming'

Humans are changing Earth's climate. How fast can we stop the damage?

The idea of 'pipeline warming' is part of the answer to this question.

Future increases in global temperatures will be caused by greenhouse gasses that have already been released. What would happen if the clean energy transition happened overnight?

Earth's energy budget is out of balance

Humans cause global warming by trapping heat in the lower atmosphere and preventing it from escaping.

Earth's energy budget was in balance before people started burning fossil fuels to power factories and vehicles. The amount of energy coming in from the sun was the same as it was leaving.

The amount of carbon dioxide in the air is 50 percent higher than it was at the dawn of the industrial age.

The trapping of energy by carbon dioxide emissions and other greenhouse gases is equivalent to the detonation of five atomic bombs per second.

Earth's thermal energy increases due to more energy coming in than leaving.

Warming in the pipeline

Time is needed for the effects of tampering with Earth's energy balance to be seen. It takes time for the warm water to get to you because the pipes are full of cold water. Warming hasn't been felt yet, but it is in the works.

After emissions stop, the climate is expected to continue warming.

The leading contributors to global warming are carbon dioxide and methane, which linger in the atmosphere for about 10 and 400 years, respectively. The amount of heat-trapping gases in the atmosphere doesn't decrease immediately when emissions are turned off.

(The Conversation/CC-BY-ND)

Sulfate aerosols are tiny particles emitted by fossil fuel burning that reflect sunlight out to space.

The warming effect of greenhouse emissions has been masked by the global dimming. Man-made aerosols are harmful to human health and the environment.

It takes a few tenths of a degree of warming over a decade to reach a new equilibrium.

It takes time for Earth's climate to change. Two-thirds of the Earth's surface is made of water, which is slow to absorb excess carbon and heat.

The Conversation/CC-BY-ND

About a quarter of the excess carbon has gone into the ocean.

While land-dwellers may be grateful for this buffer, the extra heat contributes to sea level rise through thermal expansion and also marine heat waves, which can disrupt the ocean food chain.

Carbon dioxide concentration is the biggest control knob for Earth's surface temperature, which is driven by the balance of energy at the top of the atmosphere.

How much warming?

How much commitment are we going to make to warming? There is no obvious answer.

The world has warmed by more than a degree. The world has been slow to react to the fact that nations agreed in 2015 to try to keep the global average from rising more than 1.5C.

It's difficult to determine the amount of warming. Climate models are used to estimate warming. Some Earth system models continued to warm for hundreds of years even after emissions were cut off.

There is a 42% chance that the world is committed to 1.5 degrees.

The amount of warming matters because the dangerous consequences of global warming don't just rise in proportion to global temperature; they typically increase tenfold.

There are tipping points in the Earth system that could cause irreversible changes. When the planet has passed a tipping point, we don't know when the changes will show up. The basis for limiting warming under 2C and 1.5C is this and other climate sensitive systems.

There are long delays between changes in human behavior and changes in the climate, and that's the heart of the climate problem.

Evidence shows that the safest route forward is to transition to a carbon-free, more equitable economy that produces less greenhouse gas emissions.

The Associate Professor of Earth Sciences is from USC.

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