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Land and Sea Surface Temperature

The combined land and sea surface temperature is what most people think of first when they hear about global warming.

2016 was the warmest year on record followed by 2017 then 2015. 2018 will most likely be the fourth hottest year on record. The last decade is the fourth in a row to be the hottest decade on record.

Although it's not expected that every month or every year will be hotter than the one before (or the hottest ever), the long term trend of an ever hotter world continues.

Each of the past four decades has been hotter than any before it in the record. You can see this in the chart below:

Surface temperature chart latest 12 months

Figure 1 | Decadal global mean surface temperature anomaly. The base period is 1881-1910. Data source: GISS NASA

The chart below shows the average of 12 months to September each year, ending with September 2018. The 12 months to September 2018 averaged 0.82 °C above the 1951-1980 mean.

Surface temperature chart latest 12 months

Figure 2 | Global mean surface temperature anomaly for the 12 months to September each year. The base period is 1951-1980. Data source: GISS NASA

This next plot is the running average of the year to date as each year progresses. The first point on each chart is the average temperature for January of that year. The second point is the average of January and February, and so on. The final point on the years that have been completed is the average temperature for that year. For 2018, the last point is the average of all months to the last one plotted.

Surface temperature chart latest 12 months

Figure 3 | Global mean surface temperature anomaly progressive year to date. The base period is 1951-1980. Data source: GISS NASA

The troposphere is the layer of air immediately above the surface which is several kilometres high. There are two measures of the troposphere that are probably the most watched in regard to global warming, the lower troposphere and the troposphere. The two most commonly quoted sources of data are those maintained by remote measuring systems (RSS) and those maintained by the University of Alabama at Huntsville (UAH).

This chart is of the lower troposphere (RSS TLT). It shows the average 12 months to September, with the last data point being the 12 months ending September this year.

RSS TTT temperature

Figure 1 | Troposphere temperature anomaly for the 12 months to September each year. The base period is 1979-1998. Data source: RSS


The El Niño-Southern Oscillation (ENSO) is an irregular pattern of shifting temperature, wind and currents in the equatorial Pacific Ocean. It is strong enough to affect global surface temperature. The ups and downs in temperature caused by ENSO events are on top of the trend of global warming.

These charts show the impact of ENSO years, with data from the Australian Bureau of Meteorology and GISS NASA. Orange bars are El Niño years (a warming effect), blue bars are La Niña years (a cooling effect). In the bottom chart the years shown by green bars have both El Niño and La Niña occurring in that year.

The sea surface temperature is recorded by buoys located all over the oceans, supplemented by data recorded by ships. The chart below shows the sea surface temperature changes reported by NOAA as ERSST v4.



Figure 1 | Sea surface temperature anomaly for the 12 months to September each year. The base period is 1971-2000. Data source: NOAA

Ocean heat content

More than 90% of the extra heat we're causing is going into the oceans. Scientists monitor the changes in ocean heat through various means, one of which is the collection of Argo floats. These are free-drifting floats with instruments that measure things like temperature and salinity. They can sink to a depth of two kilometres (about 1 1/4 miles) and then slowly rise to the surface again, where they transmit data to satellites. These data are collected and analysed by scientists around the world.

You can read more about the Argo array, and details of how the floats are constructed and operate on the Argo pages.

The oceans are heating up

This chart shows the change in heat of all the world's oceans combined since 1957. Since 1968, more than 30 x 1022 joules has been absorbed by the oceans. This is equivalent to more than 70,000,000,000,000 tonnes of TNT or 101,849,035,284,090,930 Big Macs - according to Alex Wellerstein. (That's the equivalent of more than 180,000,000 years of Big Macs sold in the USA.)

Figure 1 | Ocean heat content since 1957. Data source: NOAA

Arctic sea ice is shrinking.

Sea ice is melting in the Arctic. The chart below shows the change in sea ice extent in September, when extent is at its minimum. The period shown is from 1953 to 2018. The data was provided by Dr Walt Meier of NSIDC, and I've updated it with data from NSIDC. The period from 1953 to 1978 is based on Hadley ISST version 1, with values adjusted to be consistent with Sea Ice Index via method referenced in the publication:

Meier, W. N., Stroeve, J., Barrett, A., and Fetterer, F., A simple approach to providing a more consistent Arctic sea ice extent time series from the 1950s to present The Cryosphere, 6, 1359-1368, doi:10.5194/tc-6-1359-2012, 2012.


Arctic sea ice extent September




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