A new draft report developed by scientists from thirteen federal government agencies and released this week states that the average temperature in the United States has risen rapidly and substantially since 1980, and that it is “extremely likely” that nearly all of the global mean temperature increase since 1951 has been caused by human activity.
The report directly contradicts statements by the Trump Administration that the causes of global warming are uncertain, and that the impacts of climate change are impossible to predict.
According to the report, global annual temperature has increased by more than 1.6°F from 1880-2015, and average temperatures are higher than at any time in the last 1700 years. The report states that from 1951-2010 the average global mean temperature increase was 1.2°F, and the human contribution to warming during the same period was 1.1° to 1.3°F.
In the United States, the largest changes since 1900 have occurred in the western United States, where average temperatures increased by more than 1.5°F. The chart at left shows annual temperature differences from the average temperature from 1880-2015. Red bars show temperatures above the average for the period, and blue bars show temperatures below the average. Note that since 1980, not only have temperatures been above average every single year, but average temperatures have increased throughout the period.
What’s more, according to the report, “global climate is expected to change over this century and beyond. Even if humans immediately ceased emitting greenhouse gases into the atmosphere, existing levels would commit the the world to at least an additional 0.5°F of warming over this century relative to today.”
If the report is correct, humans can control the amount of warming that occurs by emitting less greehouse gas into the atmosphere, with the magnitude of climate change beyond the next few decades determined by the amount of greenhouse gases emitted globally. Within the next few decades however, temperatures will continue to rise — at least 2.5°F — even if we decrease carbon emissions dramatically.
The two graphs above show the temperature impact of different levels of carbon emissions. The graph on the left shows projected changes in annual carbon emissions in units of gigatons of carbon (GtC) per year, and the graph on the right shows the impact of the higher and lower scenario on temperature change. The implication is clear: if we do not dramatically change the level of emissions, we could see global temperature change of up to 10°F by the year 2100. If we begin immediately to reduce emissions, we can hold temperature increases to 2°F.
Other key findings:
- Reductions in western US winter and spring snowpack are projected as the climate warms. Under high-emissions scenarios, “chronic, long-lasting hydrological drought is possible by the end of the century.”
- There will be fewer extreme cold days and more extreme hot days. The graph at right compares the average number of 100° days in Billings currently and the number that we can expect to see in future years under high emissions and low emissions scenarios. Under the high emissions scenario, we can expect nearly 50 days over 100° by the year 2100! (This model created by climatecentral.org, and not part of the federal report. To see their model for other cities, click here.)
- More than 90% of the extra heat being trapped inside the climate system by human emissions is being absorbed by the ocean, causing sea level rise. Global mean sea level has risen by about 8-9 inches since 1880, with about 3 inches of that rise occurring since 1990. Relative to the year 2000, sea level is very likely to rise by 3.6-7.2 inches by 2030; 6-14.4 inches by 2050; and 1-4 feet by 2100. In most projections, sea level will continue to rise beyond 2100 and even beyond 2200.
- Because human activity is the primary cause of climate change, limiting global warming to 2° will require major reductions in emissions. Atmospheric levels of carbon dioxide have now passed 410 parts per million, the highest since the Pliocene Era, approximately three million years ago, when global mean temperatures were 3.6° to 6.3°F higher than they are today.
There is much more in the report, and I recommend you read it. We have much to do if we are going to avoid climate disaster.
And to those of you who will write to tell me that this is a bunch of nonsense: this is science. The authors of the report are leading climate scientists who have employed the scientific method. The data that they analyzed is available to anyone who would like to analyze it and reach a different conclusion.
But keep this in mind: the planet is warming without any consideration for how people feel about science, politics, or religion.