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OPINION | ART HOBSON: Tipping points signal the catestrophic threats of global warming

Sixteen tipping points threaten future generations by Art Hobson | September 20, 2022 at 1:00 a.m.

Mother Earth has finally awakened most of us to the reality of global warming. As epic wildfires, unprecedented flooding, record heatwaves and devastating droughts strike around the world, extreme weather dominates the news.

For one example, the world's fifth most-populous country is fighting for its survival. Monsoon rains delivered five times Pakistan's normal amount of water. The country's glaciers are melting at rates never seen before. The resulting super flood has ravaged the entire nation. Fifty million are internally displaced, millions are homeless, a malaria epidemic threatens, a huge new inland lake has formed and famine looms.

UN Secretary-General Antonio Guterres calls for financial support from rich countries, saying "This is not a matter of generosity, it's a matter of justice." Pakistan's carbon emissions are 0.4 percent of the total, while U.S. emissions constitute 21 percent.

Germany's Potsdam Institute for Climate Impact Research issued a report, published a week ago in Science magazine under the title "Exceeding 1.5 C global warming could trigger multiple climate tipping points." The phrase "1.5 C global warming" means 1.5 Celsius (2.7 Fahrenheit) degrees above pre-industrial temperatures.

The report studies "tipping points" that occur when a particular change, such as Greenland ice sheet melting, becomes self-perpetuating -- beyond human control regardless of our future reductions of carbon emissions. Ice sheet melting, for example, reinforces itself when melting ice uncovers dark earth or dark water because dark surfaces absorb more sunlight than icy surfaces. By studying the relevant climate literature, the study's 10 authors identified 16 such tipping points, nine of them having global impact and seven having regional impact.

Three tipping points are the most dangerous because they have global implications and come at less than 2 C global warming: Collapse of the Greenland Ice Sheet, collapse of the West Antarctic ice sheet and collapse of ocean circulation in the Labrador Sea (between Canada and Greenland). These three tipping points will be reached at a global warming of 1.5 C, 1.5 C, and 1.8 C, respectively. However, the "error bars" on all three estimates are about 0.5 C, leading the report to conclude: "We cannot rule out that the West Antarctic ice sheet and Greenland ice sheet tipping points have already been passed."

Please re-read that last sentence, slowly.

Greenland's ice sheet covers Greenland and is 5,000 feet (almost one mile) thick. Its surface is melting, and its sides are calving. As the surface melts, it loses height and thus warms just as the Rocky Mountains are warmer at lower levels. As the sides calve, ice is replaced by open ocean and land surfaces. These effects lead to self-perpetuating feedback at about 1.5 C degrees of warming.

The West Antarctic ice sheet is "grounded" on rock lying below sea level. Thus ocean currents deliver warm water to the grounding points. This is the first step in a chain reaction: Ocean heat eats away at the ice, causing the ice shelf to lose mass (weight). The lighter ice shelf floats higher, which moves the grounding line further inland and the cycle repeats. This process eventually causes the entire glacier to lose its footing, so that it slides toward the sea and no longer holds inland glaciers back, creating sea level rise.

The Labrador Sea instability relates to the abrupt collapse of the Labrador "gyre" -- a region of downward-spiraling ocean water near the Gulf Stream, which in turn influences the entire North Atlantic and its weather patterns. Warming induces stratification (layering) of warmer regions and colder regions in the Labrador Sea. Computer models predict that this inhibits the downward spiraling of water that has been cooled by the cold temperatures near Greenland, and this produces a self-reinforcing feedback effect that disrupts the Gulf Stream within just 5 to 50 years, disrupting global weather patterns.

The Paris Climate Agreement's goal is to limit warming to below 2 C, and preferably below 1.5 C. The new study shows that even this goal is not safe, but it is much more safe than allowing warming to exceed 2 C. Currently, we are headed toward a warming of 2 to 3 C, which will trigger the three global tipping points discussed here, plus three regional ones.

The West Antarctic ice sheet holds 8 meters of sea-level rise, the Greenland ice sheet hold 6.5 meters. Passing these tipping points commits our descendants to centuries of rising seas.

We must unhook from fossil fuels. The solution most likely to work is called "carbon fee and dividend." If you want to help, look at the Citizens Climate Lobby's website,

Print Headline: Global warming arrives


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