Time is short to deal with climate

The Paris climate agreement of 2015 pledges to hold the increase in the global average temperature to “well below 2 degrees (Celsius) above pre-industrial levels.” It adds that even better would be “pursuing efforts to limit the temperature increase to 1.5 degrees.” A sensible next step then asked scientists to examine and report on the difference for the planet and its inhabitants between the two objectives.

That evaluation from the U. N. Intergovernmental Panel on Climate Change arrived earlier this month. It is the work of some 90 scientists from 40 countries. They analyzed more than 6,000 peer-reviewed scientific studies. Among the words in response to the report were “shocking,” “extraordinary,” “alarming,” “grim,” “a collective scream.” Actually, the conclusions follow from the scientific consensus of recent decades.

Every one-tenth of a degree matters when it comes to the warming planet, the mounting emissions of greenhouse gases trapping heat, as physics dictates they will.

Consider the differences in that one-half degree. The projected cost in damage from the smaller increase would be $54 trillion. The expense climbs to $69 trillion with an increase of 2 degrees. A sea-ice-free Arctic summer would go from once a century to once per decade. The Great Barrier Reef, around for 25 million years, would die, as opposed to shrinking 70 percent to 90 percent.

Marine fisheries would double their rate of decline. An additional 420 million people would be at risk of exposure to extreme heat. If the planet already is seeing the harm from climate change in rising seas (eight inches since 1880) and more episodes of extreme weather, the fallout will accelerate as the warming goes from the current 0.8 degrees to 1.5 and then 2.0.

As things stand, the planet is on a course to 3 degrees Celsius by the end of the century — even if every country meets its Paris commitment. Which puts a more realistic projection at 4 degrees.

Nathan Hultman of the Brookings Institution frames the trend in a way that should motivate action. In an essay last week, he noted the difference in the global average surface temperature between the last ice age and today — around 4 degrees to 7 degrees. He adds that is not that different from what the planet now faces.

Hultman also points out that to get on a path to no more than a 1.5-degree increase requires reducing current greenhouse emissions 60 percent by 2030 — or 12 years.

With that challenge in mind, the U. N. climate panel explained that the effort involves transforming the global economy at a speed and scale with “no documented historic precedent.” The size of the task makes all the more distressing the stance of the Trump White House, including its withdrawal from the Paris agreement. It also makes plain the need for emphasizing what a proper response looks like, among other things, the leading economies seeking to organize a global carbon tax regime, mobilizing more resources for research and development of clean-energy innovations and putting at the front the opportunities for prosperity in such big change.

This isn’t about just adapting to 1.5 degrees or 2 degrees warmer. As the climate panel makes clear, the upward trend won’t stop until greenhouse emissions are reduced drastically.