Beyond Paris, Part 3: Overshooting Dangerous Warming Likely, But For How Long?
- Jun 11, 2014 8:00 pm GMTJul 7, 2018 8:47 pm GMT
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By Matthew Stepp and Amanda Kibbe, Center for Clean Energy Innovation
In 2012, Jesse Jenkins and Matthew Stepp took stock of the global climate policy challenge in an online series titled The Future of Global Climate Policy. Since then the Intergovernmental Panel on Climate Change (IPCC) completed its Fifth Assessment and many countries are taking stock of their existing—and some argue, failed—climate policies. Looking to the future, the latest round of international climate negotiations is set to close in Paris at the end of 2015, potentially offering the end of one era of global climate policymaking and the start of something new. With an eye on the long-term impacts of the 2015 negotiations, Amanda Kibbe and Matthew Stepp take an updated look in a five-part series on the state of the climate challenge. For Part 1, click here. For Part 2, click here.
Solving climate change is an extremely difficult—even monumental—challenge to address. Carbon emissions come from burning fossil fuels and are deeply embedded in the global economy. Turning on the lights, driving vehicles, powering industry, and living a prosperous life all emit carbon. As a result, cutting global carbon emissions is not a simple task and with each passing year the number of pathways to mitigating climate change dwindles. In fact, the scientific community indicates that mitigating climate change is still possible, but will most likely result in exceeding “dangerous” levels of carbon emissions in the short and mid-term followed by historically unprecedented decarbonization rates and the use of carbon removal technologies.
The IPCC goes into detail on whether and how the world can solve global climate change in part three of their Fifth Assessment report on mitigation. Scientists have built sophisticated, and increasingly complex, computer models of the global climate system, which are used to predict what the future climate might look like depending on how fast, slow, deep, or shallow the world cuts carbon emissions. The IPCC reports on over 900 different carbon reduction scenarios, which it uses to estimate how much carbon reduction is needed to keep global average temperatures within 2°C warmer than pre-industrial levels, the globally accepted, but arbitrarily set limit for what society deems “dangerous climate change.”
In Part 2 of this series, we summarized why the status quo is unacceptable moving forward. To keep temperatures from exceeding 2°C warming, the IPCC estimates that CO2 concentrations should not exceed 450 ppm by 2100. Currently, global emissions are hovering around 400 ppm and are rising fast—carbon emissions have risen faster from 2000 to 2010 than in the previous three decades. Between 1970 and 2010, emissions from fossil fuel combustion were responsible for about 78 percent of this increase (the remaining largely from land-use change). And under the status quo, emissions will continue to rise, and by 2100, temperatures will increase 3.7°C to 4.8°C warmer compared to pre-industrial levels.
Keeping concentrations below 450 ppm by the end of the century requires substantial cuts in carbon emissions. According to the IPCC, global CO2 emissions must decline 90 percent between 2040 and 2070, and should be near or below zero by 2100. Any delay in reducing emissions in the short-term reduces our ability to keep temperatures below 2°C, and requires adapting to a fundamentally different planet than what humans are accustomed to.
No doubt, this resolution is daunting, particularly because the two main drivers of fossil fuel consumption—population and wealth growth—are increasing as well. Global population nearly doubled since 1970 (3.7 billion to 6.9 billion) and is forecasted to increase by up to 28 percent by 2040. Global wealth—defined as GDP per capita—is forecasted to increase by roughly 127 percent by 2040. The challenge becomes even more difficult if the world aggressively addresses global energy poverty and provides access to the 1 billion or more that have none or little access to energy at all.
These trends will have significant impacts on energy demand and, therefore, carbon emissions if the world continues to use fossil fuels. Power and transportation sector CO2 emissions are expected to double by 2050 compared to 2010 levels. Buildings and industrial sector CO2 emissions are expected to increase between 50-150 percent during the same period.
According to the IPCC’s carbon reduction models, keeping global emissions to 450 ppm even with global population and wealth growth is possible, but it’s going to be very difficult. The majority of reduction scenarios produced in the IPCC report cannot realize the short-term carbon emission reductions needed to stabilize around 450 ppm. Instead most model simulations forecast “overshoot,” where global carbon concentrations exceed 450 ppm (often up to 530-580 ppm), but by the end of the century fall back to around 450 ppm after a low-carbon global energy transformation and the deployment of “carbon dioxide removal” technologies. In all scenarios that stabilize global concentrations at around 450 ppm, deep carbon cuts of 40 to 70 percent compared to 2010 are needed by 2050. And if the world waits until after 2030 to start cutting global emissions, the rate of reductions after 2030 must double to roughly 6 percent per year, a rate of decarbonization never seen before in recent human history.
It’s particularly important to put an even finer point on the scale of this challenge compared to current efforts. Stabilizing carbon emissions around 450 ppm requires large scale changes to global and national energy systems in the coming decades. This includes tripling or quadrupling renewable, nuclear, and carbon capture technology by 2050 compared to 2010 levels. Reducing emissions through energy demand, such as energy efficiency, plays a role, but is not sufficient by itself. And the modest voluntary carbon reduction pledges made by countries during international climate negotiations are completely incompatible with any scenario for stabilizing emissions at 450 ppm.
It’s clear that 2°C warming limits set by the climate community has a high likelihood of being surpassed and it’s no longer whether we can avert 450 ppm, but whether we can limit how long we exceed those levels. The majority of focus by the international climate community has rightfully been on mitigation and clean energy technologies. But the most viable pathways to addressing climate change now also include the development of scalable carbon removal technologies and advancing global adaptation efforts as quickly as possible.