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.

If you live in the eastern half of the United States, you may find the warmth of 2014 a little surprising. Most of 2014 was not remarkably warm in this part of the world. In some states in the Midwest, 2014 was actually one of the top 10 coldest years on record.How can this be? I’m shivering as I read this!

This region, however, was not representative of the rest of the world. In fact, the eastern United States was one of the few places on the planet where 2014 registered as a below-average year (or even a near-average year; see map).

Most of the world experienced above-average temperature (denoted by the red shading). The eastern United States was one of the few locations exhibiting below-average temperature (shown in blue). SOURCE: NOAA

Scientists draw on observations from weather stations, ships, buoys, and satellites to weave together a coherent picture of Earth’s temperature. Although temperature estimates from before the satellite era may be subject to greater uncertainty than our current temperature estimates, there is a lot of agreement among independent scientific groups that maintain global temperature sets. For example, the estimates and trends in the temperature records compiled by NOAA, NASA, the United Kingdom’s Met Office, and Japanese Meteorological Agency are nearly identical.Just how do we take the Earth’s temperature?

Annual temperature estimates from different research groups are very similar, and the trends are nearly identical. SOURCE: NASA

The record-hot year is one indication of our warming planet, but other evidence is all around us: rapidly melting ice sheets and glaciers, changes in growing seasons, and plant and animal species moving to higher altitudes and latitudes. It all paints a clear picture of a changing climate, and underscores the urgent need for stronger efforts to curb carbon emissions.