Is climate change really happening?

17 May 2016

Question

I have watched a youtube video called The Great Global Warming Swindle, which puts forward convincing evidence that there is no correlation between CO2 levels and rising temperatures. Featured on the programme are Nigel Lawson, Nigel Calder (ex New Scientist Editor), Patrick Moore (founder of GreenPeace). They actually show graphs that say that over long periods of time, temperatures rise and THEN, 800 years later CO2 levels rise. They also show eveidence that states in the 1940s to 1970s when CO2 levels rose significantly, temps dropped. They also show a direct correlation between temperature rises and sun spot activity. How can climate change scientists refute these facts? Please explain. Thanks Hywel Jones

Answer

Dan Jones seperated fact from fiction...

Dan - Whenever I think about climate change I don't usually start with the temperature trend, like you're suggesting, I'd start with carbon dioxide. We know that carbon dioxide is a greenhouse gas that was measured in the mid 1800s and any spectroscopy lab in the world can see the wavelength of radiation that carbon dioxide likes to absorb and emit. We know that it absorbs every from the earth's surface and then emits energy back down to the earth's surface.

Chris - By energy you mean heat? To make it simple. We're talking about basically infrared energy aren't we. Heat?

Dan - Yes, infrared, that's fine.

Chris - So what you're saying is the more CO2 that there is because it can absorb more of that energy, there's more opportunity for that energy to be soaked up?

Dan - If you put more CO2 in the atmosphere you will get more energy down here at the surface, that's really clear. We've been adding about 30 billion tons of carbon dioxide per year and that accumulates in the ocean, atmosphere, and land and that's from fossil fuel burning. The short story is that that energy has to go somewhere. If you double carbon dioxide that's energetically equivalent to putting a 4 watt light bulb on every square metre of the earth's surface and letting it run 365 days a year, 24/7. 4 watts might not sound like a lot but the earth is gigantic, so if you put one of these light bulbs in every square metre, that ends up being energetically equivalent to about 40 nuclear explosions per second, which is.

Chris - Okay. So the physics argument is that because there's more of something that can soak up the energy around there should, therefore, be more opportunity to interrupt that energy before it goes off into space and the earth's system should become warmer, so that's what the physics says. But what people are saying is when you look at graphs and things like that there appears to be some disparity between what the carbon dioxide's doing, what the temperatures doing, what the current climate measurements and predictions are doing. How do climate scientists like you respond to those sorts of allegations?

Dan - Right. What the gentleman who asked the question was referring to was the surface temperature - just land surface temperature. Well not just land but the surface temperature and that quantity can be affected by how energy is exchanged between the atmosphere, and the ocean, and the cryosphere. So, if that's the only number you're looking at you will see some wiggles, it will rise, it will fall and some of that is just due to exchanges of energy between the different parts of the climate system. An easier to read thermometer, I might suggest, would be something like ocean heat content. It takes more energy to raise the temperature of the ocean by 1 degree than it does the atmosphere because you can put a lot more heat into the ocean - it has a higher heat capacity. So, if you look at the ocean heat content for the past several decades, it has been increasing and it looks steadier than the surface temperature, which does have some of these increases and decreases.

Chris - So, is it fair to say that the general trend is an upward one for both the surface temperature and also the sea temperature? That there are fewer wiggles in the sea than there are at the surface, which you would expect because the ocean it takes a lot more energy in the ocean so it's going to be a lot more stable over time? We would expect to see wiggles in the atmosphere because there are going to be changes and variations year on year anyway, but the general trend is an upward one?

Dan - That right, so I wouldn't get too caught up in looking at one year or even a couple of years. I'd look at several decades, the past century or so.

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