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As we smash the record yet again for the hottest month on record, making it all but inevitable that 2016 is the warmest year on record, it seems likely that we are going to miss the target to limit global warming to within 1.5°C (2.7°F) of the average. Yet just how far back in time do we have to go to find a year when the global surface temperatures were not above the average?

Well the answer is nowhere near as simple as the question belies. There are many yardsticks by which to measure the warming of the planet, something that is not helped by the fact that different organizations are using different sticks. You have to determine whether you are talking about a warming over the land, over the ocean, or over both the land and the ocean. All three will give you a different answer. Not to mention that this is then compounded by the fact that you can break it down geographically, looking at the Northern Hemisphere, Southern Hemisphere, and once again at both.

More confusingly, even if you choose to look at the warming over land and sea in both hemispheres, there are still different baselines by which to measure exactly how much warmer the planet has become over the last century and a half.

 

Global temperatures above the 1880-1899 average. NASA
If we consider the baseline as being the average temperature taken between 1880 and 1899, which is generally considered when the warming of the planet really started to ramp up as the Industrial Revolution kicked off and we began burning fossil fuels and spewing millions of tonnes of carbon dioxide into the atmosphere, the last year that the global temperature was not above average was back in around 1936. This means you would have to be over 70 years old to have experienced a below-average year.

If you use data from NASA, however, you’ll get another answer. They use an average taken between the years of 1951 and 1980, which we have to remember already contains a certain amount of warming from the previous hundred years. With this data set then, the last year that the planet was below average is a lot later at 1976, which means that you would have to be over 40 to have been alive during a year that was not above the average.

While there have been many peaks and troughs over the past century and a half, all the data agree on a single undeniable fact: There has been a steady rise in global temperatures since the Industrial Revolution, and this rise has increased rapidly within the last half-century. It is a trend that will continue to rise unless something is done soon.


Global temperatures above the 1951-1980 average. NASA

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