Goodbye one point five

The most prominent climate scientist in North America says the planet has kissed goodbye to the target of keeping global warming below 1.5C. James Hansen says the drastic temperature spurt over the last half year makes this clear.

“By May the 12-month running-mean global temperature relative to 1880-1920 should be +1.6-1.7°C and not fall below +1.4 ± 0.1°C during the next La Nina minimum,” Hansen and colleagues write in a paper released on January 4. “Thus, given the planetary energy imbalance, it will be clear that the 1.5°C ceiling has been passed for all practical purposes.”

December global average temperatures smashed records for the seventh straight month. Hansen’s group says this is partly because of a “moderately strong El Nino” but that is less significant than a sharp change in the reflective capacity of the planet.

“The earth has become darker”, conclude the scientists, because of “reduced sea ice cover and reduced cloud cover”. They point to the ocean around Antarctica where “sea ice cover was at the lowest point in the period of satellite data.” Ice and snow are highly reflective of sunlight while darker surfaces like the ocean absorb the warmth of that incoming solar radiation.

They also point to the impact of rapidly melting icebergs and glaciers which “cool the ocean surface creating a heat sink, as a large amount of energy is needed to melt the ice. This heat sink and cool ocean surface increase Earth’s energy imbalance.”

Hansen told the UK Guardian in the only mainstream coverage to date: “We are not moving into a 1.5C world, we are briefly passing through it in 2024. We will pass through the 2C (3.6F) world in the 2030s unless we take purposeful actions to affect the planet’s energy balance.”

Some leading climate scientists are not convinced global temperatures won’t fall back below the 1.5C target, but most acknowledge that it will be decisively exceeded by early next decade.