How we can keep global warming below the 1.5 degrees Celsius goal – The Washington Post
whether their homes will continue to exist.” class=”wpds-c-hcZlgz wpds-c-hcZlgz-bkfjoi-font-georgia wpds-c-hcZlgz-jDmrXh-width-mdCenter wpds-c-hcZlgz-iPJLV-css mw-md pb-md font–article-body font-copy ma-auto pl-sm pr-sm”>It’s the world’s most important climate goal: limiting the Earth’s warming to 1.5 degrees Celsius (2.7 Fahrenheit). It’s the aspiration of global agreements, and to inhabitants of some small island nations, the marker of whether their homes will continue to exist.
avoid further destabilizing Antarctica and Greenland, staving off dramatic sea level rise.
But with the world having already warmed by more than 1.1 degrees Celsius (2 degrees Fahrenheit) above preindustrial temperatures, achieving the goal is in grave doubt.
a key 2022 report of the U.N. Intergovernmental Panel on Climate Change.” class=”wpds-c-hcZlgz wpds-c-hcZlgz-bkfjoi-font-georgia wpds-c-hcZlgz-jDmrXh-width-mdCenter wpds-c-hcZlgz-iPJLV-css mw-md pt-lg pb-md font–article-body font-copy ma-auto pl-sm pr-sm”>To see what hope remains, The Washington Post examined over 1,200 different scenarios for climate change over the coming century, based on the models produced by the world’s leading climate scientists and considered in a key 2022 report of the U.N. Intergovernmental Panel on Climate Change.
Potsdam Institute for Climate Impact Research in Germany, we explored the central features of these scenarios — how fast the world embraces clean energy, how quickly we can remove greenhouse gases from the atmosphere — and looked at how these in turn affect the planet’s temperature over the course of the century.” class=”wpds-c-hcZlgz wpds-c-hcZlgz-bkfjoi-font-georgia wpds-c-hcZlgz-jDmrXh-width-mdCenter wpds-c-hcZlgz-iPJLV-css mw-md pb-md font–article-body font-copy ma-auto pl-sm pr-sm”>Working with experts from the Potsdam Institute for Climate Impact Research in Germany, we explored the central features of these scenarios — how fast the world embraces clean energy, how quickly we can remove greenhouse gases from the atmosphere — and looked at how these in turn affect the planet’s temperature over the course of the century.
The results, as you will see, show a world that keeps inching closer to catastrophic climate change. But they also point a way toward a less hot future. The scenarios help show us what needs to be done — and what we can still do.
Out of more than 1,200 scenarios — some with temperatures rising as high as 5°C above preindustrial levels — 230 paths leave our planet below 1.5°C before the end of the century.
scenarios, which were finalized in 2021 at the latest, increasingly conflict with reality. After all, the world just saw emissions rise in 2022.” class=”wpds-c-hcZlgz wpds-c-hcZlgz-bkfjoi-font-georgia wpds-c-hcZlgz-jDmrXh-width-mdCenter wpds-c-hcZlgz-iPJLV-css mw-md pb-md font–article-body font-copy ma-auto pl-sm pr-sm”>But when we look at those scenarios that have the temperature closing out the century below 1.5C, there is a big problem. With their dramatic plunges in greenhouse gas emissions levels by 2025 — just three years away — some of the scenarios, which were finalized in 2021 at the latest, increasingly conflict with reality. After all, the world just saw emissions rise in 2022.
Next, we take out the scenarios that conflict with near-term reality, leaving 112 paths that get us to 1.5°C by 2100.
dangerous tipping points and even calamities such as the irreversible loss of the West Antarctic ice sheet.” class=”wpds-c-hcZlgz wpds-c-hcZlgz-bkfjoi-font-georgia wpds-c-hcZlgz-jDmrXh-width-mdCenter wpds-c-hcZlgz-iPJLV-css mw-md pt-lg pb-md font–article-body font-copy ma-auto pl-sm pr-sm”>There are two different kinds of scenarios that leave the planet, in the year 2100, below 1.5C of warming. One involves a “high overshoot,” but spending decades above 1.5C in such a world is an unsettling prospect. It raises the possibility, for instance, of the world experiencing dangerous tipping points and even calamities such as the irreversible loss of the West Antarctic ice sheet.
If we look closely at the 112 hopeful paths, we see two narratives. In high overshoot, the Earth’s temperature leaps far above 1.5°C before coming back down again.
These 26 paths rely on negative emissions technologies to reach net zero around mid–century, and then go farther.
method developed by the Potsdam Institute researchers and their international colleagues to filter scenarios based on the kinds of future developments they anticipate and the speed of progress they show happening.” class=”wpds-c-hcZlgz wpds-c-hcZlgz-bkfjoi-font-georgia wpds-c-hcZlgz-jDmrXh-width-mdCenter wpds-c-hcZlgz-iPJLV-css mw-md pt-lg pb-md font–article-body font-copy ma-auto pl-sm pr-sm”>To assess how realistic these scenarios are, The Post used a method developed by the Potsdam Institute researchers and their international colleagues to filter scenarios based on the kinds of future developments they anticipate and the speed of progress they show happening.
energy transitions and carbon removal technologies, and applied their expert judgment to define the thresholds. They also had to remove a small number of scenarios that did not have enough information to be analyzed by these methods (about 10 percent of the total).” class=”wpds-c-hcZlgz wpds-c-hcZlgz-bkfjoi-font-georgia wpds-c-hcZlgz-jDmrXh-width-mdCenter wpds-c-hcZlgz-iPJLV-css mw-md pb-md font–article-body font-copy ma-auto pl-sm pr-sm”>On five criteria, these scenarios are rated as “speculative,” “challenging” or “reasonable,” in order of increasing plausibility. In judging where to draw the lines, the scientists reviewed existing studies on topics such as energy transitions and carbon removal technologies, and applied their expert judgment to define the thresholds. They also had to remove a small number of scenarios that did not have enough information to be analyzed by these methods (about 10 percent of the total).
Reasonable, challenging or speculative?
Potsdam Institute researchers rated 1.5°C scenarios as speculative, challenging, or reasonable on these five dimensions, based on progress by 2050:
As we begin to apply these filters, we see how the paths to meeting 1.5C narrow. Let’s consider “reasonable” expectations for the world’s ability to remove carbon dioxide from the air and store it underground — which in many ways is the biggest variable affecting whether the world can still hold warming below 1.5C without a major overshoot. Then we’ll require scenarios to be “reasonable” on the four other dimensions too.
When we change the assumption to reasonable for carbon dioxide removal and storage underground, four paths to 1.5°C remain on the chart. And when we look at only reasonable assumptions, there is no path left.
What the results suggest is that the world has probably run out of easy options to stay under 1.5C — or have a low overshoot.
So that leaves two sets of other scenarios to consider, if the world wants to end the century below 1.5C somehow.
Still looking at low or no overshoot scenarios, we can bring back 11 paths by choosing challenging assumptions instead of only reasonable ones.
