Can We Still Limit Global Warming to 1.5°C? Here’s What the Latest Science Says
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The Intergovernmental Panel on Climate Change (IPCC) is set to release its synthesis of the Sixth Assessment Report early next week. Among the thousands of questions the report addresses by summarizing the latest climate research, one of the most hotly debated is this: Is it still possible to limit future global warming to 1.5°C above pre-industrial levels? Or has that ship sailed?
These assessments tell us that, in theory, there is still a path we could forge that would enable us to limit future warming to 1.5°C or less. In reality, we are dangerously far from that path, and we will likely exceed the 1.5°C limit in the next 10-15 years. Warming beyond the 1.5°C mark, however, would bring us closer to dangerous tipping points and accelerate severe climate impacts, so even if we know we’re likely to overshoot that mark, we have to keep aiming for it.
We are here, just a few tenths of a degree away from the 1.5°C mark, because of decades of inaction on the part of policymakers and decades of deception and obstruction on the part of fossil fuel companies. To secure the livable future that children around the world deserve, we must double down, ratchet up pressure on governments, and break the power of the fossil fuel industry.
Why is 1.5°C an important global warming limit?
The goal of limiting future warming to 1.5°C or less above pre-industrial levels is a cornerstone of the Paris Agreement—one that was hard won by an alliance of small island states and the least developed countries around the world who considered it to be a relatively sufficiently safe limit to future warming, given the existential threats they face. Research on the differences in impacts between a 1.5°C warming and a 2°C warming has largely confirmed that view. As first reported in the IPCC’s Special Report on Global Warming of 1.5°C, this half-degree increment represents the difference between losing 70% of the world’s coral reefs and losing 99% of them; having an ice-free Arctic Ocean once every 100 years or once every 10 years; and exposing 271 million people to water scarcity vs. 288 million. Even our current level of warming—about 1.1°C—is taking a heavy toll on lives, homes, livelihoods, and ecosystems around the world.
With the increased severity of impacts associated with warming beyond 1.5°C, and with those impacts falling hardest on people in countries that have contributed the least to the climate crisis, 1.5°C is both a meaningful guardrail for our climate and a powerful rallying point for advocates of climate action.
What does the latest science tell us about 1.5°C goal?
Whether it is advisable to limit future warming to 1.5°C is unquestionable. Whether it is possible, however, depends on how you define “possible.”
Modeling highlighted in the IPCC’s Working Group III report shows that global emissions would need to peak before 2025 and decrease by 43% relative to 2019 levels by 2030 to have a roughly 40% chance of limiting future warming to 1.5°C with limited or no overshoot.
But emissions are still rising…
These modeling pathways assume that emissions reductions begin just after 2020. While global emissions did drop (by about 7%) in 2020 as a result of the COVID-19 pandemic, they rebounded in 2021. Between 2021 and 2022, global emissions from energy sources and industrial processes grew by nearly 1% and preliminary data suggests that US emissions grew by an estimated 1.3%. In other words, the immediate action these modeling pathways required has not been taken.
…and without stronger policies, global emissions are likely to continue to grow.
Under the Paris Agreement, countries around the world have made voluntary pledges—called Nationally Determined Contributions, or NDCs—to reduce their emissions. In its most recent Emissions Gap report, which assesses potential outcomes based on NDCs, the United Nations Environment Programme (UNEP) found that emissions need to decrease to about 33 GtCO2e per year by 2030 to stay within the 1.5°C limit. If the current NDCs were fully met, annual emissions in 2030 would be more than 50 GtCO2e and warming would reach about 1.8°C. However, countries are far off track for even meeting the NDC pledges because there is a gap between the pledges that have been made and the policies that have been implemented. With current policies, emissions in 2030 would be roughly 58 GtCO2e globally.
And then there are aerosols…
These estimates leave out an important feedback process that will make it even harder to stay within the 1.5°C limit. In addition to releasing greenhouse gases, burning fossil fuels releases aerosols that actually have a cooling effect on the planet. Without those aerosols the warming we have experienced to date would have been even larger. And because ramping down our emissions from fossil fuels will also ramp down the resulting aerosols, their cooling effect is expected to decrease as we decrease our fossil fuel use. That feedback process will dampen the benefit emissions reductions have on global temperature changes.
The IPCC and UNEP reports spell out exactly what would have to happen to have a fighting chance of staying within the 1.5°C limit. A fighting chance is still a chance, of course, and perhaps there is a world in which immediate, deep, sustained emissions reductions take root within the next two years and lead to a near halving of global emissions this decade. But history, political reality, and current commitments to date suggest that such a future is unlikely.
Why are we on the brink of 1.5°C of warming?
It’s been almost 33 years since the first IPCC report was issued. Instead of triggering a global wake-up call to policymakers around the world, global emissions have only increased since then—by a whopping 54%. It’s not a lack of information or a lack of actionable science that’s lead to this inaction. Rather, the inaction is a product of policymakers’ indifference and prioritization of short-term wins over long-term needs, and the fossil fuel industry’s deep-pocketed deception and obstruction. Those two forces of inaction are far from separate, of course, with fossil fuel companies having unfettered access to policymakers.
To be perfectly clear, in the face of clear communications about the science for more than 30 years, policymakers around the world—and particularly policymakers in wealthier countries such as the United States—have failed to meet calls to action made by scientists as well as communities already being affected by climate change. The fossil fuel industry has also played a critical role by deliberately deceiving the public about the causes and consequences of continued fossil fuel use, by doubling down on a business model tailor-made to wreak havoc on the planet, and by staunchly opposing climate action at any level.
What do we do now?
Additional warming beyond the 1.5°C mark would bring us closer to dangerous tipping points, discontinuities, and feedback loops associated with an exponential acceleration of impacts. Many of these would initiate along the path between 1.5°C and 2C of warming, so it is imperative that we continue to aim to limit warming to as close to 1.5°C as possible.
In other words, even if we know it’s unlikely we’ll be able to hold warming to 1.5°C or less, we need to behave as if we can hold warming to 1.5°C or less—while also preparing communities for a more dangerous world where we have blown past that.
What that means is that we need rapid, transformational changes across the global economy in every sector within this decade. We must slash emissions quickly and wealthier nations like the United States must lead both in emissions reductions and in providing financial support to low- and middle-income countries to help them get onto low-carbon, clean energy trajectories as well. The IPCC Working Group III report finds that “current financial flows fall well short of the levels needed” to achieve emissions-reduction goals, particularly in developing countries.
We must also cease building out additional fossil fuel-based infrastructure that will lock in future emissions. I’m writing this just days after the Biden Administration approved the massive, decades-long Willow oil drilling project in Alaska; this is the kind of thing that we simply can’t afford to do anymore.
The fossil fuel industry has, for decades, opposed and obstructed any meaningful action on climate change. And despite ardent claims otherwise, the industry has refused to commit to align its business model with what the IPCC says is required to minimize climate harms. The industry remains a barrier to the future the world’s children deserve. Having refused to lead the way to a clean energy future and refused to follow others who see the potential for that future, we must get the industry out of the way and hold it accountable for its decades of deception and obstruction.