DAILY SCIENCE

What if the standard way of planning climate mitigation is part of the problem?
In order to do right by the younger generation, scientists and policy makers need to change the way they study climate change and plan mitigation strategies.
September 24, 2019

Last Friday, an estimated 4 million people around the world took part in a global climate strike, organized and led by teenagers and young adults who say that the lack of action on climate change has compromised their future.

On Monday, a paper in Nature argued that the standard way of studying climate change and planning mitigation strategies is part of the problem. In order to do right by the younger generation, scientists and policy makers need to revamp their approach.

Most climate modeling studies use the year 2100 as their endpoint. Scientists game out different scenarios for how and when the nations of the world could reduce carbon emissions in order to limit global warming to 1.5 or 2 °C, the benchmarks specified in the 2015 Paris Agreement, in the year 2100.

The new study suggests that scientists should run climate models with a different question or goal in mind: how to reach peak warming as fast as possible, while keeping peak warming within the 1.5 or 2 °C guardrails.

The basic problem with the current approach is that it gives rise to scenarios involving a period of “overshoot” in which global average temperature rises above the target levels for a few decades around mid-century before being brought back down again.

Such scenarios imply that we can keep doing what we’re doing for a while longer and kick the climate mitigation can down the road. That’s probably a comforting thought, but it is profoundly unfair to the younger generation, whose adult lives would be shaped and constrained by dangerous warming during that “overshoot” period.

In addition, these scenarios often imply that meeting the Paris Agreement goals requires substantial use of negative emissions to remove excess carbon dioxide from the atmosphere. Such strategies include widespread tree planting and use of bioenergy, which some researchers have suggested could compromise other goals such as food security and protection of natural ecosystems, and direct air capture, which is unproven.

So, since negative emissions strategies are themselves problematic, this in turn gives rise to the perception that meeting the Paris Agreement goals is infeasible anyhow.

In short, the current modeling approach “may encourage risky pathways that delay action, reach higher-than-acceptable mid-century warming, and rely on net removal of carbon dioxide thereafter to undo their initial shortfall in reductions of emissions,” the researchers write.

Instead, the new approach homes in on achieving global net zero emissions as fast as possible. That in turn will bring about peak warming as soon as possible.

“The need to stabilize warming more quickly is paramount, and therefore we suggest a focus on reaching net zero carbon emissions as a key milestone of any climate strategy,” lead author Joeri Rogelj said in a statement.

To do all that will require rapid decarbonization starting immediately – which of course will be no easy feat. But this approach rightly puts intergenerational justice front and center, Rogelj and his colleagues say.

This new logic for running climate change models is also more in line with the Paris Agreement, which does not emphasize 2100 in relation to its overall goal and suggests that 1.5 and 2 °C should be considered benchmarks for maximum warming, the researchers argue.

And it decouples negative emissions from maximum warming. The researchers run some calculations using well-known computer climate models and standard socioeconomic development scenarios to explore how their approach works. They show that if peak warming is small and happens sooner, temperature could subsequently be brought down without massive deployment of negative emissions. So there’s good news at the end of the heavy lift.

Source: Rogelj J. et al.A new scenario logic for the Paris Agreement long-term temperature goal.” Nature 2019.

Image: sasastro via Flickr.

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