Scientists Revise Climate Change Scenarios as Some Extremes Seem Unlikely

In recent developments, researchers have dropped their worst and best case scenarios for climate change as they seem no longer plausible. This highlights modest progress in curbing climate change while also confirming the challenge of meeting the 2015 international warming goals.

Scientists have put forward seven new plausible carbon emission scenarios, moving away from extreme outcomes. Changes in energy sources have led to this shift. The burning of fossil fuels like gas, oil, and coal still drives warming. Yet, increased use of renewable energy such as solar, wind, and geothermal has cut the high-end carbon emission predictions. Progress is slow, though, which keeps the lower-bound projections from dropping significantly.

The Paris climate agreement set a target to limit warming to 1.5 degrees Celsius since pre-industrial times. This goal is unachievable according to new best case scenarios, which slightly exceed this mark. Simultaneously, the foreboding 4.5 degrees Celsius increase from a coal-heavy future no longer seems likely.

The revised worst case scenario projects about 3.5 degrees Celsius warming by the end of the century, a reduction from previous estimates. Meanwhile, the best case scenario suggests warming above the Paris target, with a slight uptick. As Detlef Van Vuuren, climate scientist from Utrecht University, outlines, this results in a narrower range of potential futures. Cooking and spike temperatures are inevitable, but unlikely to be extreme.

Johan Rockström, director of the Potsdam Institute for Climate Impact Research, highlights a new middle scenario predicting 3 degrees Celsius warming by century’s end. This aligns with current emission trajectories. Earth, currently at 1.3 degrees Celsius above pre-industrial levels, faces new challenges as additional warming causes ecosystem disruptions and intensifies extreme weather.

Achieving the 1.5 degree goal appears impossible as global carbon emissions persist. Even in the best case, warming breaches the 1.5 degree mark and peaks at 1.7 degrees Celsius for up to 70 years. This emphasizes the need for carbon removal technologies, which presently lack feasibility.

Bill Hare, CEO of Climate Analytics, asserts that the failure to control warming reflects a political shortcoming, not an inevitable catastrophe. It’s crucial for policymakers to act swiftly.

Cornell University’s Natalie Mahowald, co-author of a U.N. report, underscores the significance of the 1.5-degree goal, stressing its impact on small island nations.

Revisions to the highest warming scenario continue to spark debate. Roger Pielke Jr. of the American Enterprise Institute notes that previous high-end predictions, dubbed RCP8.5, were improbable due to outdated assumptions. Yet, they greatly influenced climate studies.

Keywan Riahi, who introduced this scenario, clarified it represented an unlikely worst-case estimate at the time. Thanks to the plummeting costs of renewables, this scenario now seems less likely.

Despite acknowledging the progress, climate scientist Van Vuuren warns of persisting significant risks. While society avoided the most hazardous emissions trajectory, it isn’t free from adverse climate impacts.

Yet concerns linger over nature’s influence on climate dynamics. Phenomena such as climate feedbacks and natural carbon releases could exacerbate warming beyond emissions alone, potentially adding up to half a degree Celsius more warming.

As climate challenges evolve, scientists stress the importance of prompt and effective climate policies.