22 September 2013
The Real Uncertainties In Climate Change
Posted by Dan Satterfield
The Intergovernmental Panel on Climate Change (IPCC) will release its 5th assessment report next Friday in Sweden. It’s the work of over 200 scientists, who have put together a summary of the peer-reviewed science published over the last several years, and it will almost certainly be bad news.
You’re almost certain to hear some very ridiculous things in the coming days by those who fear the consequences of reducing our use of fossil fuels. It amazes me how a deeply held political view can cause someone (with virtually no background in atmospheric physics) to tell every major scientific body on the planet they are wrong. What’s more, they are totally blinded to the fact of how insanely ridiculous they look in doing so.
Someone asked me last week “if these people didn’t drive me crazy”, and I told them that actually it was just the opposite. It’s served as a very valuable lesson to me. A bright red warning that making decisions based on real facts, and being prepared to change any opinion when new information comes in is a rare asset. This ability is perhaps one of the greatest attributes of a science education, because that in itself embodies the scientific method. Remember my favorite (and often repeated) quote by Dr. Neil de Grasse Tyson that “The great thing about science, is that it’s true, whether or not you believe it”.
So here are some of the silliest things you will hear in the coming weeks, and just so you know, they are all ridiculously false. Most of them laughably so.
1. It’s the sun! (We know for certain that it has not caused more than a fraction of the warming.
2. We are still warming up after the ice age! (Temperatures peaked several thousand years ago when humans were living in caves.)
3. The warming has stopped! The planet is cooling! (This is most popular right now because air temperatures have not risen as fast in the last few years as they did in the late 1990’s. Most of the planets heat resides in the oceans, and they are indeed warming. Internal climate oscillations will continue even as greenhouse gases rise. We are getting less daylight everyday now that fall has arrived in the northern hemisphere, but it was warmer today than it’s been all week! The temperature doesn’t drop a little every day as we approach winter. The same is true of our climate.)
UPDATED: 4. The Arctic sea ice is recovering! Australian John Cook of Skeptical Science posted this graph that shows how laughably silly that one is: (I have updated the graphic below with the new one through 2013. It was made by Dana Nuccitelli.
5. Antarctic ice is increasing! (No, it’s not. The glaciers are melting rapidly from below. Ocean ice has changed little, and while complicated, the reasons are understood well.)
These are just a sampling, and one thing you might notice is that in almost every instance the person repeating them has little or no background in atmospheric science (and in some cases they sit on the science committee in the Congress!). If they do, then you should ask why they have not published their data in a peer-reviewed journal. There are dozens of great blogs about climate science written by those who work in the field. A good example is Real Climate, and John Cook’s Skeptical Science is another one.The leading blog for those who think the IPCC and NASA,NOAA etc. are all wrong is written by someone with virtually no science background at all.
That should tell you something.
The Real Uncertainties
One of the best methods of determining the rate and magnitude of the greenhouse warming is by looking at how the temperature changed in the deep past when greenhouse gases rose and fell. The ice cores from Greenland and Antarctica tell us that our 21st century models are fairly good at estimating the future, and the past. They are not perfect though, and one of the biggest uncertainties is how the physics in clouds will affect the warming. The ice cores tell us that we will warm, but getting ever more accurate predictions requires a better understanding of the radiation physics of clouds. THAT is the biggest uncertainty in climate science. What you will see online (and on some cable news channels) are the silly claims I mentioned above.
Climate Desk flew along on a NASA mission to better understand what is called the “indirect cloud effect”. See their video below:
The Graph below is from the last IPCC report. It shows how all the forcings add up and where the uncertainties are.
I leave you with my favorite and most silly reason that climate change isn’t happening.
Carbon Dioxide only makes up 400 parts per million of the air and it’s impossible for such a tiny amount to have an effect on the planet!
The truth: That tiny amount of CO2 keeps the planet about 30C warmer than it would otherwise be. With no greenhouse gases, our planet would be an ice-cube.
Sorry, but that graph ignores the Greenhouse gas gorilla in the room: Water vapor. Water makes up ~29ºC of the Earth’s GHG total, and ~163 of the 165 watts/square meter of the infrared radiative forcing. You need to read up some more about this topic.
This is still such a popular myth and the best response is what John Cook at Skeptical Science wrote several years ago about it. Reproduced in full from his website below:
Read and understand. It’s quite interesting.
Water vapour is the most dominant greenhouse gas. The greenhouse effect or radiative flux for water is around 75 W/m2 while carbon dioxide contributes 32 W/m2 (Kiehl 1997). These proportions are confirmed by measurements of infrared radiation returning to the Earth’s surface (Evans 2006). Water vapour is also the dominant positive feedback in our climate system and a major reason why temperature is so sensitive to changes in CO2.
Unlike external forcings such as CO2 which can be added to the atmosphere, the level of water vapour in the atmosphere is a function of temperature. Water vapour is brought into the atmosphere via evaporation – the rate depends on the temperature of the ocean and air, being governed by the Clausius-Clapeyron relation. If extra water is added to the atmosphere, it condenses and falls as rain or snow within a week or two. Similarly, if somehow moisture was sucked out of the atmosphere, evaporation would restore water vapour levels to ‘normal levels’ in short time.
Water Vapour as a positive feedback
As water vapour is directly related to temperature, it’s also a positive feedback – in fact, the largest positive feedback in the climate system (Soden 2005). As temperature rises, evaporation increases and more water vapour accumulates in the atmosphere. As a greenhouse gas, the water absorbs more heat, further warming the air and causing more evaporation. When CO2 is added to the atmosphere, as a greenhouse gas it has a warming effect. This causes more water to evaporate and warm the air to a higher, stabilized level. So the warming from CO2 has an amplified effect.
How much does water vapour amplify CO2 warming? Without any feedbacks, a doubling of CO2 would warm the globe around 1°C. Taken on its own, water vapour feedback roughly doubles the amount of CO2 warming. When other feedbacks are included (eg – loss of albedo due to melting ice), the total warming from a doubling of CO2 is around 3°C (Held 2000).
Empirical observations of water vapour feedback and climate sensitivity
The amplifying effect of water vapor has been observed in the global cooling after the eruption of Mount Pinatubo (Soden 2001). The cooling led to atmospheric drying which amplified the temperature drop. A climate sensitivity of around 3°C is also confirmed by numerous empirical studies examining how climate has responded to various forcings in the past (Knutti & Hegerl 2008).
Satellites have observed an increase in atmospheric water vapour by about 0.41 kg/m² per decade since 1988. A detection and attribution study, otherwise known as “fingerprinting”, was employed to identify the cause of the rising water vapour levels (Santer 2007). Fingerprinting involves rigorous statistical tests of the different possible explanations for a change in some property of the climate system. Results from 22 different climate models (virtually all of the world’s major climate models) were pooled and found the recent increase in moisture content over the bulk of the world’s oceans is not due to solar forcing or gradual recovery from the 1991 eruption of Mount Pinatubo. The primary driver of ‘atmospheric moistening’ was found to be the increase in CO2 caused by the burning of fossil fuels.
Theory, observations and climate models all show the increase in water vapor is around 6 to 7.5% per degree Celsius warming of the lower atmosphere. The observed changes in temperature, moisture, and atmospheric circulation fit together in an internally and physically consistent way. When skeptics cite water vapour as the most dominant greenhouse gas, they are actually invoking the positive feedback that makes our climate so sensitive to CO2 as well as another line of evidence for anthropogenic global warming.
Last updated on 26 June 2010 by John Cook.
A couple of corrections. John Cook has a physics degree, but he’s not a physicist. He’s now researching social science, in fact.
Also, I was the one who created the Arctic Escalator graphic. And it’s now updated with data through 2013.
My apologies! The graphic is a superb piece of science communication by the way!
Nice post. The only thing that isn’t quite right is the end that claims CO2 is responsible for keeping the planet 30C warmer. It is responsible for some of that warming, but water vapor is responsible for the most greenhouse warming of all greenhouse gases, as the quote in your response to Mr. Black says.
Actually that part is right. The water vapor is a function of temperature. It only magnifies the CO2.
Ah, my bad. You are correct. I was viewing it in terms of which species leads to what amount of greenhouse warming, as in Schmidt et al. (2010). Most of the water vapor in the atmosphere is a feedback to forced warmer temperatures caused by other greenhouse gases such as CO2. It just so happens that at the current temperature, the feedback is stronger than the direct CO2 forcing.
“Carbon Dioxide only makes up 400 parts per million of the air and it’s impossible for such a tiny amount to have an effect on the planet!”
The polio virus is also very small compared to my body. Therefore, I have no reason to be concerned about it. I’m glad I didn’t get that polio vaccine when I was a kid!
GOOD POINT. It illustrates how silly the claims that co2 is to small a component to have an effect.