Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Term:

Settings

Beginner Intermediate Advanced No Definitions Definition Life:

All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

What the science says...

Empirical measurements of the Earth's heat content show the planet is still accumulating heat and global warming is still happening. Surface temperatures can show short-term cooling when heat is exchanged between the atmosphere and the ocean, whic

To say we're currently experiencing global cooling overlooks one simple physical reality - the land and atmosphere are only one small fraction of the Earth's climate (albeit the part we inhabit). Global warming is by definition global. The entire planet is accumulating heat due to an energy imbalance. The atmosphere is warming. Oceans are accumulating energy. Land absorbs energy and ice absorbs heat to melt. To get the full picture on global warming, you need to view the Earth's entire heat content.

This analysis is performed in An observationally based energy balance for the Earth since 1950 (Murphy 2009) which adds up heat content from the ocean, atmosphere, land and ice. To calculate the Earth's total heat content, the authors used data of ocean heat content from the upper 700 metres. They included heat content from deeper waters down to 3000 metres depth. They computed atmospheric heat content using the surface temperature record and the heat capacity of the troposphere. Land and ice heat content (the energy required to melt ice) were also included.

Figure 1: Total Earth Heat Content from 1950 (Murphy 2009). Ocean data taken from Domingues et al. 2008.

A look at the Earth's total heat content clearly shows global warming has continued past 1998. So why do surface temperature records show 1998 as the hottest year on record? Figure 1 shows the heat capacity of the land and atmosphere are small compared to the ocean (the tiny brown sliver of "land + atmosphere" also includes the heat absorbed to melt ice). Hence, relatively small exchanges of heat between the atmosphere and ocean can cause significant changes in surface temperature.

In 1998, an abnormally strong El Nino caused heat transfer from the Pacific Ocean to the atmosphere. Consequently, we experienced above-average surface temperatures. Conversely, the last few years have seen moderate La Nina conditions which had a cooling effect on global temperatures. And the last few months have swung back to warmer El Nino conditions. This has coincided with the warmest June-August sea surface temperatures on record. This internal variation where heat is shuffled around our climate is the reason why surface temperature is such a noisy signal.

Figure 1 also underscores just how much global warming the planet is experiencing. Since 1970, the Earth's heat content has been rising at a rate of 6 x 10²¹ Joules per year. In more meaningful terms, the planet has been accumulating energy at a rate of 190,260 gigawatts. Considering a typical nuclear power plant has an output of 1 gigawatt, imagine 190,000 nuclear power plants pouring their energy output directly into our oceans.

How do we find out what's happened from 2003 until now? Unfortunately, there is no time series (that I know of) of the planet's total heat content up to present time. However, we do have the next best thing. Schuckmann 2009 analyzes ocean temperature measurements by the Argo network, constructing a map of ocean heat content down to 2000 metres. This is significantly deeper than other recent papers that focus on upper ocean heat, only going down to 700 metres. They constructed the following time series of global ocean heat:

Figure 2: Time series of global mean heat storage (0–2000 m), measured in 10⁸ Joules per square metre.

Globally, the oceans continued to accumulate heat right to the end of 2008. Over the last 5 years, the oceans have been absorbing heat at a rate of 0.77 Watts per square metre. Combined with the results of Murphy 2009, we now see a picture of continued global warming.

How does this value compare to other estimates of energy imbalance? Willis 2004 combines satellite altimetry with ocean heat measurements to find an ocean warming rate of 0.85 Watts per square metrefrom 1993 to 2003. Hansen 2005, using ocean heat data, calculated the planet's energy imbalance in 2003 to be 0.85 Watts per square metre. Trenberth 2009 examined satellite measurements of incoming and outgoing radiation for the March 2000 to May 2004 period and found the planet accumulating energy at a rate of 0.9 Watts per square metre.

These results all find broad agreement and all find a statistically significant positive energy imbalance. Our climate is still accumulating heat. Global warming is still happening.

Updated on 2011-11-02 by John Cook.

Climate Science Glossary

Term Lookup

Settings

Term Lookup

Settings

Latest Posts

Archived Rebuttal

What the science says...