climate science

It's certain: The Earth is getting warmer, and human activity is largely to blame

The case for climate action is having a hard time in Washington these days. While public officials acknowledge the climate is changing, they’re not necessarily saying why or what should be done about it.

Let’s clear up a few points.

 

1.The Earth is heating up.

Scientists have measured global temperatures for over a hundred years and see that the Earth is getting hotter. The trend can be best visualized by comparing each year’s average temperature with the long-term average. This figure shows observations of the world’s annual average temperature made by the National Oceanic and Atmospheric Administration (NOAA). It compares each year’s temperature to the average over the entire century. Blue bars are years that were cooler than average and red bars are years that were warmer than average. In recent decades, the years have always been hotter. If there were no long-term temperature trend, you would expect a mix of red and blue bars throughout the record. That’s not what we see.

Source: The National Oceanic and Atmospheric Administration (NOAA)

 

2. Human activity is largely responsible for this warming.

Over geologic time, the Earth’s average temperature has changed as a result of the sun’s output, the tilt and position of the Earth in its orbit, and the concentration of greenhouse gases. Scientists have developed a good understanding of the natural variations in these factors by examining different proxies for ancient temperatures. Observations tell us that these natural factors have not been changing over the last hundred years or so in a way that would explain the observed temperature increases.

In contrast, greenhouse gases have been changing in a way that can explain the observed temperature increases. The pre-eminent record of modern atmospheric carbon dioxide (CO2) concentrations is based at the Scripps Institute of Oceanography. Researchers there have been sampling pristine air from a mountaintop in Hawaii every month since 1958 and analyzing its composition. Their observations show that both the concentration and isotopic composition of CO2 is changing, and is consistent with manmade sources, including the carbon emissions from burning fossil fuels.

Moreover, physics tells us how different climate variables will change the temperature of the atmosphere at different heights. For example, changes in solar output will heat the atmosphere uniformly, while changes due to greenhouse gases will warm the surface but cool the higher part of the atmosphere (the stratosphere).

The National Centers for Environmental Information, run by NOAA, conduct monthly observations of atmospheric temperatures at different levels. Its 39-year record shows that the temperature change is not uniform. This is consistent with the effect of greenhouse gases, and inconsistent with other types of natural effects (e.g., changes in the sun’s output).

 

3. The impacts of climate change are growing, and we need to stop adding to the problem.

The result of this buildup of greenhouse gases is that we’re trapping heat within the climate system. The basic physics behind this has been establish for over 100 years. But climate change isn’t just a matter of the air temperature being a few degrees warmer.

Some observed climate changes are not bad. For example, growing seasons are lengthening in some parts of the country and costs for winter heating go down when temperatures are mild. But the overall impacts are estimated to be negative and costly.

The good news is that we’re making progress, and that we have many of the tools right now to make a difference, including expanding use of renewable power; zero-carbon nuclear power, carbon capture, use and storage; energy efficiency technologies, and electric vehicles. Many businesses, cities, and states are pursuing clean energy and clean transportation to improve public health, save money, and create jobs.

The question is not whether climate change is happening, but what we want to do about it.

Understanding climate change, even if you're not a scientist

A catchphrase has cropped up in discussions about climate change: “I’m not a scientist…”

You hear it from some elected leaders opposed to taking action to reduce climate risks. It’s usually followed by an argument that climate science is too hard to understand or there’s not enough information that climate change is a serious problem.

With this in mind, we’ve revamped our Science and Impacts webpages to ensure we’re providing understandable, up-to-date climate science information so that anyone can connect the choices we make in producing and consuming energy to the risks of climate impacts.

The State of the Climate

As President Barack Obama prepares to deliver his State of the Union address, we believe it’s a good time to take a look at the state of our climate: the growing impacts of climate change, recent progress in reducing U.S. emissions, and further steps we can take to protect the climate and ourselves.

The consequences of rising emissions are serious. The U.S. average temperature has increased by about 1.5°F since 1895 with 80 percent of this increase occurring since 1980, according to the draft National Climate Assessment. Greenhouse gases could raise temperatures 2° to 4°F in most areas of the United States over the next few decades, bringing significant changes to local climates and ecosystems.

Getting clear on climate facts

With the Intergovernmental Panel on Climate Change (IPCC) poised to release its Fifth Assessment of the science underpinning our understanding of climate change, it’s useful to take a step back and recap some of the “big picture” facts.

What is already clear from the science:

  • Carbon dioxide and other greenhouse gases act to warm the planet.
  • Carbon dioxide is accumulating in the atmosphere due to emissions from human activities.
  • The Earth has been warming during the past century. The amount and speed of the warming is unusual compared to past records.
  • Humans’ emissions of greenhouse gases are largely responsible for this warming.
  • If emission rates continue, the warming in the 21st century will be much more significant than the warming in the previous century.
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