Claim: There’s no evidence that the global climate is warming. Why worry about a problem that’s invisible?
Fact: Just about any aspect of climate you care to look at does show signs of global warming.
The US National Oceanic and Atmospheric Administration have recently released their 20th annual State of the Climate report. The report is ostensibly about the climate in 2009, but because 2009 was the end of a decade the authors decided to take a longer-term view.
According to the press release, the report
draws on data for 10 key climate indicators that all point to the same finding: the scientific evidence that our world is warming is unmistakable. More than 300 scientists from 160 research groups in 48 countries contributed to the report, which confirms that the past decade was the warmest on record and that the Earth has been growing warmer over the last 50 years.
I haven’t read the full report (it’s 200 pages long), but I have read the very accessible 10-page summary. It examines the trends for the aforementioned 10 climate indicators using a total of 47 different sets of data. As shown in the diagram at the top of this page, all of the indicators expected to increase in a warming world, are in fact increasing, and all that are expected to decrease, are decreasing.
“The analysis brings together multiple observational records from the top of the atmosphere to the depths of the ocean,” says NOAA administrator Jane Lubchenco. “The records come from many institutions worldwide. They use data collected from diverse sources, including satellites, weather balloons, weather stations, ships, buoys and field surveys. These independently produced lines of evidence all point to the same conclusion: our planet is warming.”
Although contrarians often try to frame the climate discussion as being about land surface air temperature as measured by weather stations, it was only one of the indicators used by NOAA in this report. They also looked at sea surface temperature, air temperature over the oceans, and the temperature of the lower troposphere. In fact, by just about any measure, temperatures are rising — the one major exception being in the stratosphere, which is expected to cool and accordingly is cooling. Although temperature is the most obvious thing to watch, Arctic sea ice, glaciers, ocean heat content, sea level, and humidity are all moving in the direction predicted by the global warming hypothesis.
“When we look at air temperature and other indicators of climate, we see highs and lows in the data from year to year because of natural variability,” says Peter Stott of the UK Met Office. “Understanding climate change requires looking at the longer-term record. When we follow decade-to-decade trends using multiple data sets and independent analyses from around the world, we see clear and unmistakable signs of a warming world.”
The 2000s was the warmest decade globally, and each of the last three decades has been much warmer than the previous one. Although the 1980s was the warmest decade at the time, every year of the 1990s was warmer than the average temperature of the 1980s, and every year of the 2000s was warmer than the average temperature of the 1990s. In the last 50 years the Earth’s surface has warmed by about 0.6°C, and we are already seeing the effects.
More than 90% of the extra heat from global warming is going into the oceans, because water has a much higher capacity to absorb heat than does air. Most of the increase in ocean heat content has been in the upper oceans, but heating has also been observed as far down as 2 km. The thermal expansion caused by this heating is partly responsible for the observed sea level rise.
Other findings in the full report include that Arctic sea ice had its third lowest minimum on record; and according to preliminary data, 2009 was the 19th consecutive year in which there was a net loss of ice from glaciers worldwide. Oh, and (it almost goes without saying) there’s the never-ceasing accumulation of greenhouse gases in the atmosphere. As the report summarises:
The IPCC conclusion that “warming of the climate system is unequivocal” does not rest solely upon LSAT [land surface air temperature] records. These constitute only one line of evidence among many, for example: uptake of heat by the oceans, melting of land ice such as glaciers, the associated rise in sea level, and increased atmospheric surface humidity. If the land surface records were systematically flawed and the globe had not really warmed, then it would be almost impossible to explain the concurrent changes in this wide range of indicators produced by many independent groups. The observed changes in a broad range of indicators provide a self-consistent story of a warming world.
I recommend that people read the 10-page summary — on page 3, there is a nice clear graphic showing the trends for all the different indicators. You can also look at the differences between datasets for each indicator here.
You can find previous posts in my ongoing series debunking the arguments against global warming here.