The December 2015 Paris Climate Change Agreement set out that the 196 signatories would not let the global temperature rise more than 1.5 to 2 degrees Celsius from pre-industrial levels in order to combat climate change. 1.5 to 2 degrees doesn’t sound like much but in actuality, a global rise of a few degrees would be catastrophic for our planet. But what is the difference between keeping the temperature at a 1.5 degree increase or keeping it at a 2 degree increase? Does 0.5 degree Celsius (0.9 degree Fahrenheit) really make a difference?
The European Geosciences Union released a study in April of 2016 to look at the differences between a 1.5 degree temperature increase and a 2 degree temperature increase. Overall, the study found that going from 1.5 to 2, an increase of one third, will result in a third stronger impact across the world. For example, heat waves would last a third longer, rainstorms would be a third more intense and sea levels would increase by a third.
Dave Schimel, a supervisor with JPL Carbon Cycle and Ecosystems group, explains why a half degree could be more catastrophic than it sounds. He said, “Most of that temperature change may occur during a small fraction of the year, when it actually represents conditions that could be 5 or 10 degrees warmer than pre-industrial temperatures instead of just 1.5 or 2 degrees warmer.”
Temperature Impact On Our Waters
The study revealed that with a 1.5 degree increase, tropical coral reefs may stand a chance at surviving. They could adapt to new water temperatures and regrow portions that have died due to coral bleaching. But with a 2 degree increase, this regrowth and recovery is impossible. By 2100, tropical coral reefs will be completely extinct. Michelle Gierach of JPL explained, “Reef-building corals are extremely vulnerable to warming. Prolonged warming harms warm-water corals not only through bleaching, but also through making them more susceptible to disease.”
With a 1.5 increase, areas in the Mediterranean will have to survive with 9% less fresh water. But at a 2 degree increase, the Mediterranean sees an 18% decrease in fresh water.
When it comes to rising sea levels, Felix Landerer, who studies sea level and ice at JPL, explains just how dangerous a 2 degree increase could be. He said, “I would frame the discussion in the context that in recent studies—in particular of ocean-ice interactions—there is growing concern that the ice sheets are very sensitive to the surrounding ocean warming. At two degrees (of temperature increase), you might have crossed a threshold for significantly more sea-level rise than indicated [in the current study]. The air temperatures level off, you (hypothetically) stabilize them, but you have committed to sea-level rise over multiple centuries. So it's good to stay away from two degrees. That's an experiment you don't want to run. Because that experiment would potentially wipe Florida off the map.”
Temperature Impact On Agriculture
With a 1.5 degree increase, global production of wheat and soy may actually increase thanks to the warmer temperature being favorable for farming and fertilization. However, if that increase rises to 2 degrees, the advantage for soy crops drops by 700% and is non-existent for wheat.
In many places around the world, wheat and soy plants are already near their thermal limit. In addition, the increase in temperature may also increase the spread of pests and pathogens. Therefore, even the 1.5 increase could be very dangerous, but nothing compared to the 2 degree increase.
Schimel from JPL explains the effects of the temperature rise on crops such as corn. He said, “If you get really high temperatures or very dry conditions during critical parts of the development of the crop, it produces essentially no grain. For example, above certain temperature thresholds, corn doesn't die but it doesn't grow seed. It doesn't grow a corn cob. And other crops are similar to that, where the development of the actual food part of the crop is dramatically inhibited above critical temperatures. [The fertilization effect from carbon dioxide] does help a bit, but it doesn't make the underlying problem go away. And by the way, if the plant was growing really fast when it died, it still died.”