Five key takeaways from the 5th National Climate Assessment

The National Climate Assessment is the U.S. government’s periodic report on “climate change impacts, risks and responses.” The Fifth such report, released on November 14, 2023, highlights the severity of the impacts of climate change that are already affecting people and ecosystems throughout the country and the actions and adaptations that can help the U.S. respond.

Like previous editions, the Fifth National Climate Assessment emphasizes the need to reduce greenhouse gas emissions, protect wild lands and oceans, and preserve biodiversity. The report dedicates an entire chapter to transportation – a sign of transportation’s status as the nation’s leading source of greenhouse gas emissions and the transformational changes underway in that sector. 

The report demonstrates that we have the tools we need to reach climate goals, but we must implement them much more quickly.

It’s important reading. But for those who might not have the chance to read it, here are five top takeaways:

Climate change is hurting people and ecosystems.

From the redwood forest to the Gulf Stream waters, climate change-associated disturbances are putting humans, wildlife and ecosystems at risk. Oceans and marine life are “exhibiting major divergences from historical patterns.” This includes changes in the “timing and length of seasonal cycles, the extent and duration of sea ice, the oxygen content of ocean waters,” the severity of extreme weather, the distribution of sea life populations, those populations’ ability to reproduce, and the timing of marine species’ life events. (Chapter 10) Specifically, those impacts include declining populations of salmon along the coasts of Alaska and Washington, the loss of kelp habitat in California, and the loss of coral habitat off Hawaii and Florida. Climate-related changes to ocean habitats, including coral reefs, seagrass beds and kelp forests, threaten our coasts’ ability to support ecologically important fish, turtles and marine mammals.

In America’s forests, climate change is increasing the “frequency, scale and severity” of disturbances like wildfires, insects and diseases. (Chapter 7) Wildfires are the largest contributors of one kind of air pollution in parts of the western U.S. The impacts are so severe they will likely offset improvements in air quality from reductions in human-caused air pollutant emissions by the end of the century. Climate change will likely contribute to declining air quality in many U.S. regions in the future. (Chapter 14)

We have the tools to reach net-zero emissions. They’re catching on, but not fast enough.

On U.S. emissions reductions, there is good news and bad news. The good news is that U.S. greenhouse gas emissions declined 12% between 2005 and 2019. The bad news is that’s not nearly fast enough to reach net-zero emissions by mid-century. U.S. greenhouse gas emissions would need to decline by more than 6% per year on average to reach that goal, which is based on national and international climate targets. (Chapter 32)

There is plenty of good news on the energy transition front. For starters, it is now clear that a net-zero energy system is possible in America. It can be achieved with a mix of demand-side and supply-side changes, including “widespread improvements in energy efficiency, substantial electricity generation from solar and wind energy, and widespread electrification of transportation and heating.” (Chapter 32)

Solar and wind power are expected to grow by about 325% and about 138%, respectively, by 2050. This growth was enabled by the declining cost of capital in the 2010s and continues to be supported by government subsidies, including incentives from the Inflation Reduction Act. (Chapter 5) Similarly, ocean-based renewable energy sources are expected to grow over the next several decades. (Chapter 10) However, clean energy capacity likely needs to grow even more quickly to reach the levels necessary to fully decarbonize the energy system.

Cutting climate pollution is good for our health.

Efforts to reduce emissions, including the clean energy transition and electrification of the transportation sector, can have co-benefits for public health.

Reducing emissions can improve air quality and mental and physical health, especially for city-dwellers. (Chapter 13)

Extreme heat has been linked to health problems like adverse pregnancy and birth outcomes, poorer mental health and increased emergency room visits and hospitalizations related to cardiovascular disease, diabetes, electrolyte imbalance and respiratory outcomes. (Chapter 15) Both we and future generations will benefit from actions to reduce the prevalence of extreme heat events driven by climate change.

Net-zero climate pollution is impossible without big changes in the transportation sector.

The U.S. cannot reach its mid-century net-zero goal without dramatic changes in the transportation sector, which is the largest source of greenhouse gas emissions in the country. (Chapter 13)

Based on policies in place as of November 2021, the Department of Energy projects that emissions from the sector in 2050 will be little different than they are today. Limiting global warming to 1.5℃ would require achieving net-zero greenhouse gas emissions by that year. (Chapter 13)

Decarbonizing the transportation system requires a combination of improved fuel efficiency, more stringent vehicle emissions standards, reduced passenger vehicle travel, vehicle electrification and mode switching to public transportation and walking or biking. These changes not only help to reach emissions-reduction targets but also have broad social benefits, especially in urban areas, including reductions in air pollution and extreme heat. These benefits “would accrue immediately and locally, wherever the transportation emissions changes are implemented.” (Chapter 13)

In addition to federal and state policy, local efforts can help cities and municipalities reduce greenhouse gas emissions and adapt to climate change.

Responding to climate change requires both top-down and bottom-up policies, and will require changes that occur person by person, community by community.

Communities across the country are responding to the urgency of climate change. The number of active city-level greenhouse gas emissions-reduction and climate adaptation actions in the U.S. is increasing. These local actions include renewable energy incentives, energy efficiency standards, green building incentives, community solar programs and more, often surpassing what is required by state and federal regulations. (Chapter 12)

Hundreds of local governments have drafted climate action plans and scores of cities across the country have established emissions reduction targets, including many cities in states that do not have state-level targets. (Chapter 12)

Cities and towns are also implementing nature-based solutions, such as urban forestry and green roofs, that can reduce the impact of extreme heat and flood hazards while decreasing energy demand. (Chapter 12) Other nature-based solutions, like rain gardens and urban forests, can have benefits for both climate mitigation and adaptation (Chapter 12) in every type of community, from rural areas to small towns to big cities.

***

In short, it is now clear that we have the tools and solutions we need to reach climate goals. Many of those solutions are being implemented, but the pace and scale of the change is not yet rapid enough. To get on track, we need to put all the tools we have to work as quickly as we can and at as large a scale as possible.