Global Warming

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.

2015 was the warmest year on record

Image courtesy NOAA

This visualization from NOAA shows much warmer than average or record warm temperatures across much of the globe in 2015, the warmest year on record.

The data are in, and 2015 was officially the warmest year globally ever recorded. We’ve been keeping temperature records since 1880. The last time the record was broken? 2014.

What’s interesting is just how much warmer 2015 was. The observed annual average surface temperature was more than 1.8° F (1° C) above the 19th century average, according to the National Oceanic and Atmospheric Administration (NOAA) and the National Aeronautics and Space Administration (NASA). That’s already half the warming countries have agreed to as the international limit.

And 2015 was about a quarter of a degree Fahrenheit warmer than 2014. That might seem small, but it’s actually huge when compared to the year-to-year differences observed in the record.

A strong El Niño, when the surface ocean in the Eastern Pacific basin warms, contributed to the record warmth of 2015. But even compared to other El Niño years, 2015 set records. The agencies reporting the data attribute this to the long-term warming trend due to the increase of greenhouse gases in the atmosphere.

As with all climate and weather data, the 2015 data shows some variability. Not all locations set high temperature records, and parts of the North Atlantic Ocean actually set a cold temperature record.

In the contiguous United States, 2015 was the second warmest year on record, with 2012 still holding the top spot. It was the 19th consecutive year that the annual average U.S. temperature was more than the 20th century average.

Answers to 3 key questions about the hottest year on record

Last year was the warmest globally in the 135 years since records have been kept. That was confirmed today by the National Oceanic and Atmospheric Administration (NOAA) and the National Aeronautics and Space Administration (NASA).

What’s significant about one year’s temperature?

What does one record-breaking year say about climate change? Alone, very little, but 2014’s heat did not happen in isolation. It was part of a longer streak of warm years. The last 38 years have been warmer than the 20th century average. All of the top 10 warmest years have occurred since 1998. Taken together, these warm years demonstrate that the Earth’s climate has changed and continues to change. The “warm streak” also provides a strong argument against those who claim global warming somehow stopped in the last 15-20 years. Although it is true that the rate of warming since 1998 was slower than in prior decades, the longer-term picture is unequivocal. The planet is still warming up. And as we’ve discussed previously, the ups and downs that occur over a few years or even a decade should not be used to undermine (or unnecessarily embellish) the reality of the broad warming trend.

Another interesting aspect of 2014 is that the high-temperature mark was broken without much help from El Niño. El Niño events occur when a large area of the tropical Pacific Ocean maintains above-average temperatures for many consecutive months. So, when we have an El Niño, the planet has a good chance of being warm as a whole. El Niños helped make 1998, 2005, and 2010 some of the warmest years in the temperature record. However, in 2014, ocean conditions fell somewhere between neutral and a bona fide El Niño (see NOAA’s recent blog on the state of El Niño).

Global average annual temperatures since 1880, from NOAA and The dark red columns represent the 10 warmest years in the record. 2014 is the warmest year in the record.

This winter was cold for some, not for all

A lot of folks in the eastern half of the United States are breathing a sigh of relief that spring is just around the corner. Average temperatures this winter were among the Top 10 coldest in some parts of the Upper Midwest and South. More than 90 percent of the surface of the Great Lakes is frozen, the highest in 35 years.

But while East Coast and Midwest kids have been sledding and their parents have been shoveling, it has not been cold everywhere. In fact, many areas are unusually warm.

In Alaska, January temperatures were as high as they have been in 30 years. The Iditarod dogsled race was especially treacherous this month because of a lack of snow. Crews had to stockpile and dump snow on the ground at the finish line in Nome, where temperatures earlier this winter broke a record.

Globally, January was the fourth warmest on record – really – despite pockets of well-below-normal temperatures in parts of the United States. According to the National Oceanic and Atmospheric Administration (NOAA), most areas of the world experienced warmer-than-average monthly temperatures. For example:

  • China experienced its second warmest January on record.
  • France tied its warmest January.
  • Parts of Brazil and Australia saw record heat.
January temperatures were above normal for much of the globe.
January temperatures were above normal for much of the globe.

About U.S. Federal

The Center for Climate and Energy Solutions (C2ES) seeks to inform the design and implementation of federal policies that will significantly reduce greenhouse gas (GHG) emissions, and promote clean energy. Drawing from its extensive peer-reviewed published works, in-house analyses on the design of climate change policies and clean energy policies, and tracking of current legislative proposals, the Center provides research, analysis, and recommendations to policymakers in both Congress and the Executive Branch.

The Center regularly meets with members of the federal Administration, U.S. Senate, and House of Representatives and their staff to discuss climate science, impacts, economics, policy, regulation, and legislation. C2ES also holds widely-attended Capitol Hill briefings on these topics, often bringing in experts from academia, business, and government to provide a broad range of perspectives.

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