Fourth National Climate Assessment (NCA4) – Key points

Drought in Texas
Drought in Texas

As part of an analysis of NCA4, and before this important report slides into history, let’s take a look at a summary of the overall findings. This summary includes the key findings as they relate to climate change in the U.S.


Climate change is creating new risks and increasing the problems of vulnerable communities. 

The effects of climate change are evident now and not just something to worry about in the future. Changes in average temperatures are occurring along with an increased frequency and intensity of extreme weather and climate-related events. These will continue to damage the country’s infrastructure, ecosystems and social systems. The greatest impacts will be on lower-income and marginalised communities who are less able to adapt. A reduction in greenhouse gas emissions is essential.

U.S. climate change temperatures


Unless significant effort is made to limit climate change, there will be increasing losses to infrastructure and property, and a reduction in the rate of economic growth.

Major industries such as agriculture, tourism and fisheries are particularly vulnerable to climate change. There will be higher energy costs. The effect of climate change on other countries will affect U.S. trade and economy. If emissions continue at the current rate, it is predicted that losses will reach hundred of billions of dollars by the end of the century.

Interconnected impacts

Critical systems such as water resources, food production and distribution, energy, transportation, public health, international trade and national security are all interrelated.

The effects of extreme weather and other climate-related impacts on one system can result in increased risks or failures in other systems. These interconnections are complicated and difficult to predict.

Actions to reduce risks

Communities and businesses – not just the Government – are working to reduce the risks of climate change. However, actions so far are insufficient to avoid substantial damage to the economy and human health.

In order to avoid the most severe consequences of climate change, more immediate and substantial actions have to be taken to reduce greenhouse gas emissions. 


There are increased risks to the supply and costs of water for agriculture, energy production, industry, recreation and the environment.

Rising temperatures and changes in the volume and timing of precipitation are causing intensified droughts and flooding. In some regions there is a temporal mismatch between the availability of water and its need.  There is concern about the supply of water for hydropower production. Sea level rise is the U.S. Caribbean is causing flooding and saltwater contamination.  Water management practices need to be improved.


There are increased threats to the health of the American public through poorer air quality and the increased transmission of diseases by insects and pests.

Heat-related deaths are predicted to increase, along with the frequency and severity of allergic illnesses such as asthma and hay fever.  The geographical range of diseases caused by insects is expected to widen. 

Indigenous peoples

The interconnected social, physical and ecological systems of indigenous communities face increased threats.

The livelihoods and economies of indigenous peoples depend for a great part on agriculture, agroforestry, fishing, recreation and tourism. These are increasingly threatened by climate change. Some communities are taking steps to adapt to these changes. 

Ecosystems and ecosystem services

Climate change is making transformative changes to some ecosystems such as coral reefs and sea ice. 

Many changes to ecosystems are taking place, such as the degradation of air and water quality, increased wildfire frequency, and spread of invasive plant species. These changes can only be mitigated by major reductions in greenhouse gas emissions.

Agriculture and food

Climate change is expected to increasingly disrupt agriculture in the U.S. 

Livestock health will be reduced, crop yields will drop and decrease in quality, and soil erosion will increase along with pest outbreaks. Climate change will also affect agriculture in other countries and will thereby affect U.S. trade. There are many adaptation strategies that could be adopted but their effect will be limited if climate change is severe.


Heavy precipitation events, coastal flooding, heat and wild fires will have a major effect on the country’s ageing infrastructure. 

This degradation of infrastructure, such as energy production and transportation, will threaten the economy, national security, essential services and well-being. Rising sea levels will affect the trillion-dollar coastal property market. 

Oceans and coast

The rise in sea level and high-tide flooding will increase the costs of coastal communities and lower property values

Ocean temperatures are rising and oceans are becoming acidified.  Arctic sea ice is retreating and coastal erosion is increasing. Commercial fisheries, and the communities that depend on them, will suffer.

U.S. ocean temperatures and sea level

Tourism and recreation

Outdoor recreation and tourist economies will be degraded by climate change.

Economies reliant on coral reef-based recreation, winter recreation, and inland water-based recreation, hunting and other wildlife-related activities, will all be affected by climate change.  


The threats of climate change to the U.S. could hardly be clearer or more concerning. 

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