Global warming – the basics

I’ve been getting into various online debates with climate skeptics. It typically doesn’t turn out well and eventually I just give up. It very rarely remains a discussion about the science. It often becomes pedantic or starts to become a discussion about how can we trust climate scientists given that they apparently somehow benefit from pushing a climate change agenda. I always find this an extremely odd argument given that the amount of money going into climate science is miniscule compared to the amount of money involved in the fossil fuel industry. The incentive for the fossil fuel industry to undermine arguments in favour of developing alternative energy seems much greater than the incentive for climate scientists to push some kind of agenda that isn’t supported by the scientific evidence.

Something that is regularly said is that there has been a pause in global warming since 1997. This is based on analysis of temperature anomaly data which results in a trend (since 1997) that is smaller than the 2σ errors and hence suggests that we cannot claim that there has been warming since 1997. I’ve addressed this in a number of places, but essentially this is not that surprising and there are many instances in the last 30 years where 15 years or more were needed to determine a statistically significant warming trend. Below, I’ve included a figure showing the monthly temperature anomaly data since 1880. The possible flattening in the running average (thick solid line) in the last bit of the very noisy data is what some are using to claim that there has been a pause in global warming.

1880-2012TrendNoErrors

Okay, so let’s imagine that the temperature anomaly data has indeed been flat since 1997. I’m not claiming that it has, but let’s imagine that it has. Basing whether or not global warming is happening on temperature anomaly data alone is simplistic and illustrates a lack of understanding of what global warming is at a more fundamental level. Global warming is fundamentally an energy imbalance in which we receive more energy from the Sun than we radiate back into space. In an earlier post I included a couple of figures showing that there has been a measured energy excess for 30 years or more. This tells us that global warming is happening, irrespective of what the temperature anomaly is doing. The basic point is that this excess energy doesn’t only increase surface temperatures, it also melts ice and increases the heat content of the oceans.

So, can we see evidence of excess energy going into melting the ice at the poles or into heating the oceans. Indeed we can. The figure below (taken from Stroeve et al, GRL, 39, L16502, 2012) shows September sea ice extent in the Arctic. The x-axis goes from 1900 to 2100 and the red and blue lines are from models. The black line is the observed sea ice extent and extends from 1950 to 2011. What seems clear is that the Arctic sea ice extent in September has dropped faster than even the models predicted.

Arctic sea ice extent in September (from Stroeve et al. 2012).

Arctic sea ice extent in September (from Stroeve et al. 2012).

What about the heating of the oceans? Well, the figure below shows the heat content of the oceans in Joules. It’s clear that it has been increasing pretty steadily since sometime in the 1960s. It’s also quite an impressive amount of energy. It’s increased by more than 1023 Joules since the 1960s and this is only down to a depth of 700m.

Ocean heat content (0 - 700m) from 1955 to 2012.

Ocean heat content (0 – 700m) from 1955 to 2012.

The last figure I wanted to show was one showing the heat content of the oceans and of the land and atmosphere, from 1950 to the mid 2000s. Again, they’ve both been increasing steadily since the 1960s, but the amount of energy going into the oceans dwarfs that going into the land and atmosphere.

Ocean heat content together with land plus atmosphere.

Ocean heat content together with land plus atmosphere.

So, what’s the point of this post? Well, it was simply to illustrate that global warming isn’t simply about increased global surface temperatures. Increases in the global surface temperature is what we are worried about, but global warming is a continual increase in the amount of energy being absorbed by the whole system. This includes heating the oceans and melting polar ice. The data seems to clearly indicate that the amount of polar ice is decreasing and the amount of energy going into the oceans is also increasing. This is global warming. Ignoring the oceans and the polar regions and focusing only on global surface temperatures is simplistic and shows a significant lack of understanding of what global warming is. Being skeptical of science is good. Basing skepticism on a subset of the data that doesn’t represent the whole picture is not good and if people are going to be skeptical of climate science, they should at least attempt to understand the science at some basic level.

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One thought on “Global warming – the basics

  1. After writing this post, I wonder how the excess energy going into the climate system compared with the total amount of energy generated by the world’s power stations. The bottom figure suggests we’ve added about 2 x 1023 J to the climate system since 1970. That is about 5 x 1021 J per year. According to Wikipedia the world’s power stations generates 7 x 1019 J per year. The excess energy going into the climate system every year is therefore about 70 times greater than the total amount of energy generated by the world’s power stations.

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