The UN Intergovernmental Panel on Climate Change (IPCC) recently released the first part of its newest assessment report, which presents leading experts’ latest understanding of the Earth’s climate system. The report’s message is clear: human activities are warming the planet by increasing greenhouse gas concentrations in the atmosphere, and that warming is happening even faster than previously thought.
According to the IPCC, the world will reach 1.5 degrees Celsius warming within the next decade or two, with the severity of climate impacts rising with every fraction of a degree of warming. The result: more frequent and intense heatwaves, droughts, flooding, forest fires and other extreme events. Most alarmingly, some changes will be irreversible even if emissions are drastically reduced and temperatures stabilize. For instance, ice sheets will be melting for hundreds of years, and sea levels will rise 2 to 3 meters by 2300 even if warming remains below 2 degrees Celsius, and as much as 5 to 7 meters in the report’s high-emissions scenarios.
As with every IPCC report, scientists lay out the “state of knowledge” on climate change by summarizing current and relevant findings in the field, as well as assessing the likelihood of each projection to prove true based on collected data. What distinguishes the latest report is that scientists were able to make projections of the human contribution to global warming based not only on sophisticated modeling, but also on observations of actual events.
A case in point is an observed dramatic increase of methane in the atmosphere driven by natural gas leaks and agriculture practices. While its lifetime in the atmosphere is far shorter than that of carbon dioxide, methane is far more efficient at heating it up. Therefore, controlling methane could significantly reduce global warming in the coming decades. In a separate report, the UN has found that methane reduction measures that are now technically feasible could significantly decrease emissions of this potent greenhouse gas and thereby avoid a sizeable temperature increase by 2040.
Given the IPCC report’s sobering findings, what is the best pathway forward? Per UN rules, these reports must remain neutral on climate mitigation policies and not recommend a particular course of action. But their scientific findings can be used to inform governments’ decision-making process in the context of national economic and political conditions.
Drawing on previous IPCC reports and honoring its commitment to the Paris Agreement, the White House recently announced plans to reduce carbon dioxide emissions by 50 to 52 percent in 2030 relative to 2005 levels and to ensure that 50 percent of all new passenger vehicles are electric.
While these targets are moving the U.S. toward a low-carbon economy, the federal and state governments will ultimately need to design and implement more aggressive policies to meet long-term Paris climate goals and inspire the rest of the world to do the same.
To that end, putting a price on planet-warming pollutants — primarily carbon dioxide — is widely viewed as the most efficient climate mitigation strategy. Examples include emissions-trading schemes in the European Union and China; California’s cap-and-trade program; the Regional Greenhouse Gas Initiative (RGGI) in the U.S. Northeast, and the city of Boulder’s carbon tax. While these market-based approaches represent a good start, they could become more impactful by adopting more ambitious emissions-reduction targets and covering more regions and economic sectors.
To reduce carbon emissions successfully, carbon-pricing policies must be implemented equitably, as they may have wide-ranging distributional impacts on households depending on income and consumption patterns. Therefore, the U.S. should incorporate an environmental justice agenda in its approach. An equitable policy would use revenue from a “carbon fee” to provide a “carbon dividend” to members of communities with low incomes and those that bear the greatest burden of the energy transition.
There are numerous examples of good climate mitigation policies in the U.S. at the state level, including the Massachusetts Decarbonization Roadmap developed in my home state. But addressing the climate crisis described in the latest IPCC report, and doing so equitably, will require a coordinated effort at the federal level.
Make no mistake: fossil fuels raised living standards in the U.S and much of the world, but now the U.S. needs to lead the world with technology and policy options that ultimately will eliminate greenhouse gases from power generation, industry, transportation and other activities.
At MIT, our team provides socio-economic and climate pathways to decision-makers seeking to contribute to this effort. For example, in our latest Global Change Outlook, we assess the expansion of renewable energy sources, which are expected to become a dominant source of power generation in coming decades.
We also show pathways to decarbonize industry, a process that will require different solutions, such as hydrogen-based fuels and carbon capture. In the U.S., sustained legislative policy support will be needed to realize the potential of advanced technologies to promote the growth of U.S.-based industries and a stable global climate.
The IPCC report underscores that climate change will continue to affect all of us for the rest of our lives. Humans created this climate crisis, and we will have to live with its consequences. But we still have a chance of averting the very worst impacts, and it is up to us — policymakers, industry leaders, academic experts and the general public — if our children and grandchildren will view our generation as the one that made the right choices for helping the planet. For the foreseeable future, it is the only planet that we have.
Sergey Paltsev, Ph.D., is a deputy director of the MIT Joint Program on the Science and Policy of Global Change and senior research scientist at the MIT Energy Initiative.