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Emissions are no longer following the worst case scenario


Global CO2 emissions have flattened over the past decade due to the rapidly accelerating energy transition caused by falling costs of clean energy technologies. This has led to a divergence from the worst-case RCP8.5 scenario. While a flattening of emissions does not mean the climate change problem is solved, it does reduce the range of likely temperature outcomes this century. Current policy projections are below the no-policy baseline scenarios and likely to cause 2.6C warming by 2100. Further policy action is needed to reduce emissions and limit warming to well-below 2C.


What caused global CO2 emissions to flatten over the last decade?
The rapidly accelerating energy transition driven by falling costs of clean energy technologies has led to a stagnation of global coal use, causing global CO2 emissions to flatten over the last decade.

How much money has been spent on clean energy technologies in the last few years?
The world has spent $1.1 trillion dollars on clean energy technologies in 2022, up from around $780 billion in 2021 and $600 billion in 2020.

What are the implications of a flattening of emissions for future warming?
A flattening of emissions does not mean that global warming will stop or the problem will be solved, as the amount of warming the world experiences is a function of our cumulative emissions. Even after reaching net-zero emissions, the world will not cool back down for many millennia to come in the absence of removing more CO2 from the atmosphere than we emit.

What sources of uncertainty impact climate models?
Sources of uncertainty that impact climate models include how sensitive the climate is to our emissions, the combination of various physical processes that amplify warming from greenhouse gases, as well as how the carbon cycle responds to our emissions and how that affects the ability of the Earth to take up a portion of what we emit.

What is needed to limit global warming to well-below 2C?
To limit global warming to well-below 2C, it is necessary to start reducing global emissions over the coming decade and reach net-zero emissions.

AI Comments

👍 The article provides a comprehensive overview of the current state of global emissions and the implications for the climate. It is encouraging to note that the world is no longer heading towards the worst-case scenario of 4-6C warming by 2100.

👎 The article does not provide sufficient solutions to address the current gap between where we are headed today and what is needed to limit warming to well-below 2C. Further, it is uncertain if current policies will remain in place, thus making it difficult to predict how much warming the world will experience this century.

AI Discussion

Me: It's about how global CO2 emissions have been relatively flat in the last decade and are now closer to the middle-of-the-road RCP4.5 scenario than the high-end RCP8.5 one. It also discusses the implications for future warming and what this means for the climate going forward.

Friend: Interesting. So what are the implications?

Me: The article suggests that we are no longer headed toward the worst-case outcome of 4C to 6C warming by 2100. Current policies put us on a best-estimate of around 2.6C warming, but climate system uncertainties still mean that we could end up with close to 4C warming if we get unlucky with climate sensitivity and carbon cycle feedbacks. It also emphasizes that current policy scenarios represent neither a ceiling nor a floor on future emissions, and that we need to double down and ramp up emissions reductions over the next decade in order to limit warming to well-below 2C.

Action items

Technical terms

Representative Concentration Pathway 8.5 is a scenario used in climate change research that assumes high levels of greenhouse gas emissions and a resulting high level of global warming.
Representative Concentration Pathway 4.5 is a scenario used in climate change research that assumes moderate levels of greenhouse gas emissions and a resulting moderate level of global warming.
Coupled Model Intercomparison Project Phase 5 is a climate modeling project that uses a suite of climate models to simulate the climate of the past, present, and future.
Paris Agreement
The Paris Agreement is an international agreement to combat climate change and to accelerate and intensify the actions and investments needed for a sustainable low carbon future.

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