Environment
Human life depends on an environment that can provide for the most basic human needs. But climate change is increasing the earth’s temperature, melting glaciers, raising sea levels, and likely shifting ocean currents. This, in turn, appears to be reducing biodiversity and increasing the intensity of extreme weather, such as floods, droughts, wildfires, hurricanes, and excessive heat days. The quality of the air we breathe is also critical to our existence.
Climate change and air quality are driven mainly, although not entirely, by human activity. Climate change is also creating fast-rising financial losses from property damage as well as increased prevalence of asthma, dementia, heatstroke, exhaustion, and other health ailments. Some argue that the future effects are somewhat uncertain and that future technological developments might reduce greenhouse gas emissions or offset warming with technologies that cool the earth. However, given the major risks involved and the uncertainty about future technologies, there is broad agreement that greenhouse gas emissions are a significant problem. The actions we take on climate change also have a global impact. Each country’s emissions affect everyone else, and US emissions affect our ability to lead on this issue.
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Net Greenhouse Gas EmissionsNational
Trend% of countries the US outperformsIntl. Rank
Trend1%Specific Measure:
Net greenhouse gas emissions (carbon dioxide, methane, nitrous oxide, fluorinated gases), including discharge from land use and deforestation.
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Air QualityNational
Trend% of countries the US outperformsIntl. Rank
Trend73%Specific Measure:
Annual mean concentration of particulate matter with diameter of 2.5 micrometers or less (roughly 3% of the width of a human hair).
- Mixed: the trends go in strongly opposite directions during different periods.
- Unclear: too few years of data to establish a trend.
Measures in green indicate an improving national trend or that we are outperforming at least 80% of countries.
Measures in red indicate a declining national trend or that we are outperforming less than 50% of countries.
Measures in yellow indicate stable trends or that we are outperforming 50-79% of countries.
Summary of Results
We are the world’s second-largest annual emitter of greenhouse gases and the largest cumulative emitter over the last century. While we have made some improvements, greenhouse gases accumulate in the earth’s atmosphere, so the fact that we have lowered our annual emissions means that we are only making the problem worse more slowly than in the past. We are also improving air quality, though not as fast as other higher-income countries.
Related Topics
Greenhouse gas emissions arise mainly because of economic activity—energy fuels the economy (see the Economy section). Sea level rise and extreme weather events caused by climate change are expected to create considerable migration and food insecurity, which may destabilize countries and create more international conflict (see the National Security section). Particulate matter is linked to lower birthweight and reduced cognitive function in children (see the Children and Families section) and other health effects (see Physical Health).
Other Measures Considered
The board also considered, but did not include, other measures, including the number of extreme heat days. The public did not support this additional measure either.