The Fourth National Climate Assessment Report released on November 23rd presents a strong and clear message: Climate change is already affecting every sector and region of America, and further warming will wreak havoc on our health, lands and economy.
According to the report, a consensus document supported by 13 federal agencies and departments and mandated by an act of Congress, unabated climate change will substantially damage America’s communities, economy and environment. The U.S. economy is on track to lose hundreds of billions of dollars annually by the end of the century, and in the absence of steep emissions cuts, climate change will irreparably harm ecosystems and other resource-dependent parts of the economy.
This year’s report reflects significant scientific advancements since the last assessment in 2014. It documents the role of human-caused warming in creating extreme weather events; presents impacts at a much finer, local scale; and quantifies the cost of impacts now and in the future. The report has several new chapters, assessing impacts in 10 regions and exploring topics such as how climate change will affect trade, national security and air quality.
Here are four top takeaways:
1) We are already seeing the impacts of a changing climate unfold across the United States.
The report finds that the impacts of human-caused climate change are intensifying across the country and are already compromising Americans’ well-being. For example:
Since the beginning of the 20th century, annual average temperatures have increased by 1.8˚F across the contiguous United States.
Certain types of extreme events have become more frequent, intense or long-lasting. For example, the average season length of heat waves across many U.S. cities has grown by more than 40 days over the past half century. Heavy precipitation events have become more intense and frequent in most parts of the country since 1910.
Drier conditions, as well as warming, have contributed to an increase in large forest fires in the West and Alaska over the past few decades.
Sea level along the U.S. coast has risen about 9 inches since the beginning of the 20th century.
Other stressors such as groundwater depletion and deteriorating infrastructure are compounding these impacts, creating a perfect storm that has played out in events across the United States in recent years. For example, aging storm sewer systems have amplified the effects of more frequent and intense storms, causing dangerous flooding.
2) Future climate change will disrupt lives, topple infrastructure and hurt the economy.
The report compares impacts if warming is limited to 2°C (3.6°F) versus what we’ll experience with the 5-6°C of warming we could hit toward the end of the century without aggressive emissions reductions. The authors find that the warmer it gets, the more deadly and costly it will be. For example:
Extreme heat is projected to reduce Americans’ ability to work outside by 2 billion hours per year, costing the U.S. economy $160 billion per year by late this century.
Limiting warming to 2°C would avoid thousands to tens of thousands of deaths per year from poor air quality, and prevent the loss of hundreds of millions of labor hours from extreme temperatures. The resulting economic benefits would be tens of billions to hundreds of billions of dollars per year.
Rising seas, increased storm surge and tidal flooding threaten $1 trillion in public infrastructure and private property along the U.S. coastline.
Reliable and affordable energy supplies, which underpin virtually every sector of the economy, are increasingly at risk from climate change and weather extremes.
High temperature extremes, heavy precipitation, high-tide flooding along the U.S. coast, ocean acidification and forest fires in the western United States and Alaska are all projected to increase. Land and sea ice cover, snowpack and surface soil moisture are expected to decline in the coming decades.
Some risks like forest fires will increase in parts of the country where they have been more limited to date, such as in the Southeast.
The report also concludes that climate impacts will exacerbate social inequality. For example, residents in rural communities, who often have less capacity to adapt, will be especially hard hit, given their dependence on agriculture. The urban poor could face greater exposure to heat stress if they lack air conditioning or sufficient insulation, as heat waves increase in frequency and duration.
3) Adaptation is increasing, but not enough to match escalating impacts.
The report finds that adaptation projects have increased since the Third National Climate Assessment. For example, forest managers are mapping projected stream temperatures in order to prioritize areas for coldwater fish conservation. Planners in low-lying Norfolk, Virginia plan to raise roads and structures, and construct berms to prepare for future sea level rise and flooding. Scientists are developing higher-yield, stress-tolerant crops. These proactive measures will pay off; the report finds that while adaptation projects may require upfront investments, they yield benefits in the long-term that exceed near-term costs.
However, despite this action, adaptation has not kept up to speed with escalating climate change impacts. Adaptation measures have yet to become commonplace across the United States.
4) The policy response is clear.
While the report does not offer policy prescriptions, the policy implications should be perfectly clear: The United States must move immediately to reduce greenhouse gas pollution across all sectors and regions, and reinstate executive orders created under the last administration to adapt to the warming we’ve already locked in. The United States should be working with other countries to ensure that the world can meet the global goals of the Paris Agreement on climate change. It should also cooperate with other nations on the research and development needed to achieve technological breakthroughs to reduce emissions and remove carbon dioxide from the air.
The good news is that U.S. states, cities and businesses are still moving forward with climate action, despite recent setbacks at the federal level. The recently released Fulfilling America’s Pledge report shows a growing coalition of non-federal actors in the United States determined to implement climate solutions. Other studies show the opportunities to be gained: The latest New Climate Economy report found that taking bold climate action can generate $23 trillion in value globally through 2030.
The bottom line is straightforward: Climate change is harming Americans right now and putting the stability of our economy in jeopardy. We can prevent these risks and stop them from getting worse. All U.S. leaders—from local to national, from corporations to civil society groups—need to respond in earnest and with the urgency this threat deserves.