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Seemingly small shifts have dire consequences


Climate change has been accumulating slowly but relentlessly for decades. The changes may sound small when you hear about them—another tenth of a degree warmer, another centimeter of sea level rise—but seemingly small changes can have big impacts on the world around us, especially at the regional level.

Thomas Lounis via Getty Images – The Conversation

The problem is that while the effects are small at any point in time, they do add up. These effects have now accumulated to the point that their impact contributes to damaging heat waves, droughts and extreme precipitation that cannot be ignored.

The latest report from the United Nations Intergovernmental Panel on Climate Change is more emphatic than ever: Climate change, caused by human activities such as the burning of fossil fuels, has adverse effects on the climate as we know it, and those effects are rapidly getting worse.

Earth’s energy imbalance

An excellent example of how climate change can accumulate is the Earth’s energy imbalance. I am a climate scientist and I have a new book on the subject that will be published by Cambridge University Press.

The sun bombards the earth with a continuous current of about 173,600 terawatts (12 zeros) of energy in the form of solar radiation. About 30% of this energy is reflected back into space by clouds and reflective surfaces, such as ice and snow, leaving 122,100 TWh to drive all the weather and climate systems around us, including the water cycle. Almost all of that energy is due back into space—except for about 460 terawatts.

460 terawatts remaining is the problem we face. This extra energy, trapped by greenhouse gases in the atmosphere, is heating the planet. This is the Earth’s energy imbalance, or in other words, global warming.

The illustration of the globe shows the energy going in, out and the rest trapped by greenhouse gases, going primarily into the oceans.
The outgoing radiation decreases due to the increase in greenhouse gases in the atmosphere, which leads to the Earth’s energy imbalance by 460 TW. The percentage entering into each field is indicated.
Kevin TrenberthCC BY-ND

Compared to the natural flow of energy through the climate system, 460 terawatts seems small – it’s only a fraction of 1 percent. Thus, we cannot go out and feel the extra energy. But the heat builds up, and now it has consequences.

To put that into perspective, the total amount of electricity generated worldwide in 2018 was about 2.6 TWh. If you look at all the energy used around the world, including heat, industry, and vehicles, you will find that it is about 19.5 terawatts. The energy imbalance on Earth is large by comparison.

Interfering with the natural flow of energy through the climate system is where humans leave their mark. By burning fossil fuels, cutting down forests and releasing greenhouse gases in other ways, humans are sending gases like carbon dioxide and methane into the atmosphere that trap more of that incoming energy rather than letting it radiate again.

Before the first industries began burning large amounts of fossil fuels in the 19th century, the amount of carbon dioxide in the atmosphere was estimated at 280 parts per million by volume. In 1958, when Dave Keeling began measuring atmospheric concentrations at Mauna Loa in Hawaii, that level was 310 parts per million. Today, those values ​​have risen to about 415 parts per million, an increase of 48%.

Carbon dioxide is a greenhouse gas, and increasing amounts are causing heating. In this case, the human increase is not small.

Where does the excess energy go?

Measurements over time show that more than 90% of this extra energy goes into the oceans, where it causes water to expand and sea levels to rise.

The upper layer of the oceans began to warm in the 1970s. By the early 1990s, heat reached a depth of 500 to 1,000 meters (1,640 to 3,280 feet). By 2005, it was warming the ocean below 1,500 meters (nearly 5,000 feet).

Two graphs, one of which shows the annual increase in temperature in the top 2000 meters of the ocean.  The other is colored lines that show the increase in heat on several levels.
Average global temperature change at different ocean depths, in zettajoules, from 1958 to 2020. The upper graph shows an elevation of 2,000 meters (6,561 ft) compared to the 1981–2010 average. The bottom shows the increase at different depths. Reds are warmer than average, and blues are cooler.
Cheng et al, 2021, CC BY-ND

Global sea level, as measured by flights and satellites, was rising at a rate of about 3 millimeters per year from 1992 to 2012. Since then, it has been rising by about 4 millimeters per year. At 29 years old, he has risen over 90 mm (3.5 in).

If 3.5 inches doesn’t seem like much, talk to coastal communities that are located a few feet above sea level. In some areas, these effects have led to chronic flooding in sunny daytime during high tide, such as Miami, San Francisco, and Venice, Italy. Coastal storm waves are louder and more destructive, especially than hurricanes. It is an existential threat to some low-lying island states and a growing expenditure for American coastal cities.

A portion of that extra energy, about 13 terawatts, goes to melt the ice. Arctic summer sea ice has decreased by more than 40% since 1979. Some of the excess energy is melting land ice, such as glaciers and permafrost in Greenland, Antarctica, pumping more water into the ocean and contributing to sea level rise.

Some of the energy penetrates into the ground, about 14 terawatts. But as long as the Earth is wet, a lot of the energy cycles turn into evapotranspiration — evaporation and transpiration in plants — which moistens the atmosphere and nourishes weather systems. When there is a drought or during the dry season, the effects build up on the land, by drying out and wilting plants, which leads to higher temperatures and dramatically increases the risks of heat waves and wildfires.

Consequences of more heat

Above the oceans, the excess heat provides an enormous source of moisture to the atmosphere. This becomes latent heat in storms that replaces hurricanes and rainstorms, leading to flooding, as people have suffered in many parts of the world in recent months.

The air can have about 4% more moisture for each degree Fahrenheit (0.55 Celsius) increase in temperature, and the air over the oceans is about 5% to 15% more moisture than it was before 1970. Hence, there is a 10% increase in heavy weight. It is caused by precipitation as storms collect excess moisture.

Again, this may not sound like much, but this increase activates updraft and storms, and then the storm lasts longer, so suddenly there is a 30% increase in precipitation, as has been documented in several major floods.

Satellite view of a hurricane with an outline of islands in its path
Cyclone Yasa heads for Fiji in December 2020. It was the fourth deadliest tropical cyclone on record in the South Pacific.
NASA Earth Observatory

In Mediterranean climates, characterized by long, dry summers, such as in California, eastern Australia, and around the Mediterranean, the danger of wildfires is increased, and fires can be easily ignited from natural sources, such as dry lightning or human causes.

Weather extremes have always occurred, but human influences are now pushing it beyond its former limits.

The straw that breaks the camel’s back syndrome

Therefore, while all weather events are driven by natural forcings, the impacts are greatly amplified by human-caused climate change. Hurricanes cross thresholds, dams break, and floods flow. Elsewhere, fires are out of control, things are breaking and people are dying.

I call it “the straw that breaks the camel’s back syndrome.” This is highly nonlinear, which means that risks don’t rise in a straight line – they rise faster, and this confuses economists who have greatly underestimated the costs of human-caused climate change.

The result has been very little action taken in both slowing and stopping problems, and in planning impacts and building resilience — despite years of warnings from scientists. The lack of proper planning means we all suffer the consequences.

[The Conversation’s science, health and technology editors pick their favorite stories. Weekly on Wednesdays.]

This article is republished from The Conversation, a non-profit news site dedicated to exchanging ideas from academic experts. Written by: Kevin Trenberth, National Center for Atmospheric Research .

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Kevin Trenberth has received previous grants from the Department of Energy, NASA, the National Oceanic and Atmospheric Administration, and seed funding from the National Science Foundation



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