ART HOBSON: Tipping points signal catastrophic threats of global warming

Mother Earth has finally awakened most of us to the reality of global warming. As epic wildfires, unprecedented floods, record heat waves and devastating droughts hit the world, extreme weather dominates the news.

For example, the fifth most populous country in the world is fighting for its survival. The monsoon rains provided five times the normal amount of water in Pakistan. The country’s glaciers are melting at a rate never seen before. The resulting super flood devastated the entire nation. Fifty million people are internally displaced, millions are homeless, a malaria epidemic threatens, a huge new inland lake has formed and famine threatens.

UN Secretary-General Antonio Guterres calls for financial support from rich countries, saying “it’s not a question of generosity, it’s a question of justice”. Pakistan’s carbon emissions make up 0.4% of the total, while US emissions make up 21%.

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

The report studies the ‘tipping points’ that occur when a particular change, such as the melting of the Greenland Ice Sheet, becomes self-sustaining – beyond human control, regardless of our future emissions reductions of carbon. The melting of the ice cap, for example, is enhanced when melting ice uncovers dark land or dark water, because dark surfaces absorb more sunlight than icy surfaces. By surveying the relevant climate literature, the 10 authors of the study identified 16 tipping points, of which nine have global impact and seven have regional impact.

Three tipping points are the most dangerous as they have global implications and occur within 2 C of global warming: Greenland Ice Sheet Collapse, West Antarctic Ice Sheet Collapse and Ocean Circulation Collapse 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 around 0.5C, leading the report to conclude: “We cannot rule out that the West Antarctic ice sheet tipping points and Greenland have already been exceeded”.

Please re-read that last sentence, slowly.

The Greenland Ice Sheet covers Greenland and is 5,000 feet (almost a mile) thick. Its surface melts and its flanks calve. As the surface melts, it loses height and therefore warms up just as the Rocky Mountains are warmer at lower levels. As the sides calve, the ice is replaced by open ocean and land surfaces. These effects lead to a self-sustaining feedback at about 1.5°C warming.

The West Antarctic Ice Sheet is “founded” on rocks below sea level. Thus, ocean currents deliver warm water to anchor points. This is the first step in a chain reaction: the heat of the ocean eats away at the ice, leading to a loss of mass (weight) of the pack ice. 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 seaward and no longer holds the interior glaciers, creating sea level rise.

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

The goal of the Paris Climate Agreement is to limit warming to less than 2C, and preferably less than 1.5C. The new study shows that even this goal is not sure, but it is much safer than letting warming exceed 2C. Currently, we are headed for 2-3C warming, which will trigger the three global tipping points discussed here, as well as three regional ones.

The West Antarctic Ice Sheet contains 8 meters of sea level rise, the Greenland Ice Sheet contains 6.5 meters. Passing these tipping points commits our descendants to centuries of rising seas.

We have to get off fossil fuels. The solution most likely to work is called a “carbon charge and dividend”. If you want to help, check out the Citizen Climate Lobby website,

Teresa H. Sadler