Friday, 4 February 2011

The human fingerprint in global warming?

The human fingerprint in global warming
There are highly polarised views on the subject of climate change, with extremists on both sides accusing the other of misinfomation and worse.

So I was very interested to read the article on the left here which explains the science behind the claim that human activity is contributing to climate change. Helpfully, it even gives explanations at basic, intermediate and advanced levels. And for the science buffs out there, the levels do concentrate on different aspects so all levels are worth a read.

 This prompted a good discussion with a relative who is skeptical of human influence on climate.  Neither of us are extremists, both enjoy exploring ideas, and we had an enjoyable dialogue.  So I though it may be worth relating the conversation here:

Billy: For anyone interested in the Climate Change debate, an excellent explanation of the science behind the consensus that it is caused by human activity. In basic, intermediate and advanced forms, dig as little or as much as you like!

Harvey: Ooooh scary scary - how will we cope with a degree extra over the next few decades!

Billy: Ah, no longer denying climate change, or that it is man-made, but now saying it doesn't matter. Climate skepticism to climate apathy. That's progress of a sort, I guess. ;-)

Harvey: Here is my kitchen logic:

I hope we can agree on the fact that oil will run out within circa 60 years forcing a switch to another fuel, almost certainly one that does not emit CO2. Agree?

Given that even your wildest predictions for temp rises in the next 60 years amount to not very much, what the heck is all the fuss about?

Billy: I guess the known oil reserves may well run out in 60 years, but there are ever more places opening up to exploration. Plus there extraction of coal is largely a matter of economics: as easy coal runs short, prices go up, so currently uneconomic resources become viable again. But you're right, there is a finite limit.

I don't make predictions for temp rise: I don't have the knowledge or data to make predictions. I could join you in the kitchen and make a stab at it. First of all, I'll see if I can find a published prediction with a reasonable pedigree. I'll get back to you...

Billy: Okay. Starting with the supposed link between CO2 levels and increased global temp. Bear with me, because this may give us an idea of how much warming can be expected.

The physics of CO2 heat absorption are well understood, and easily demonstrated in the kitchen. But if for a moment we set that aside, is there evidence of correlations between CO2 and temp from the past to back it up?

Vostok temp, CO2 and dust. Petit et al, 1999
I found a paper by Petit et al in Nature, (Nature 399, 429-436 3 June 1999) The important part is a chart showing changes in temperature, CO2, dust, all revealed in ice cores from the Vostok ice station in Antarctica.

There is a striking correlation between changes in CO2 and changes in temp. When CO2 rises by 100ppm, Vostok temp rises by 10°C. Now Vostok temp is not global temp, but it's a good place to start.

Take a look at the data, and the peer reviewed paper it comes from. Do you see what I see? If not, do you have similarly reputable evidence for a different conclusion?

Harvey: Like I said before, I don't buy into the causal link between CO2 and significant climate change. But suspending judgement, what is your best guess at climate change over the next 60 years...? if this is small then it doesn't matter who is right....

Billy: Did you see the chart in my previous post? Do you have better evidence to the contrary or does the evidence perhaps not matter? If you do have contrary evidence then I'd be delighted to see it.

I'm not a climate scientist, so following you into kitchen science is rather dubious, but perhaps it's the best I'm equipped to do. Taking the recorded trend showing that in the 30 years from 1975 to 2005, global average temp rose 0.6°C, then if we simply extrapolate that over the next 60 years then there could be a further rise of 1.2°C, making a 1.8°C rise since our childhoods.

You may say that 1.2°C or 1.8°C is not much, and on any individual day that may be true. But if you are familiar with the normal distribution curve, if you were to take the number of days of extreme high temp in the 2000s, (say the top 1%), shift the curve right by 1.2°C, you'll see that there is a large increase in the number of days with extreme high temp (above the same temp limit as before). Given that a heatwave in 2005 killed 3000 people in France, such a rise is anything but trivial. And that's leaving out the effects on agriculture, desertification, energetic extreme weather events, changes to the distribution of air and ocean currents and sea level rise through melting ice over land masses.

Furthermore, your assertion that we'll run out of fossil fuels in 60 years is far from certain. Known coal reserves are estimated at between 150 and 400 years, and that ignores any reserves yet to be discovered.

My projection ignores any positive feedback effects of warming, which could include the release of CO2 from thawing polar permafrost and the release of methane from the sublimation of deep ocean methane hydrates. The record from the last 420,000 years shows sharp and large temperature rises, with slower and moderate temperature falls. Such positive feedback effects could explain these sharp rises. Once the climate begins to warm, there is good reason to suspect it could continue to warm substantially, as it has before.

The climate science, based on peer reviewed scientific studies, rather than the opinion columns of novelists like James Delingpole, seem to suggest that we are indeed changing our climate. But if you choose to take your science from the Mail or Telegraph rather than Nature or Science, then I can understand your point of view.

Harvey: Yes, I did look at the chart... great to see that over thousands of years the variation in temperature was well within the range of -11 to +3°C. This is in-line with your estimate of 1.2°C rise over the next 60 years, which is pretty underwhelming.

Peak oil production. Hubbert, 1956
I also think 60 years is a pretty conservative estimate about when the oil is likely to run out: (are you really saying we will then use coal as a starting point for oil?!).

So we are left with the fear of an increase in extreme climatic events...which will never grab attention compared with the far greater and more immediate threats now facing mankind, such as Malaria or a host of preventable diseases, etc..

The church grabs our attention by suggestion we will go to hell if we don't listen to their doctrine.... which does kind of grab your attention for a few minutes. A rise in temp of 1.2C before the problem starts to go away does not grab the attention and that's why digging into the science (taking us away from our beloved Mail and Telegraph) is about as likely as a straight hockey stick ....

Billy: Ah, I think we need to understand what effect a comparatively small rise in MEAN GLOBAL temperature could have. It certainly does not mean that your peak daytime temperature in Switzerland, or mine in England, would rise by 1.2°C. That alone would be underwhelming, I totally agree with you there.

2000 year global temperature. Rhode, 2005
The mean temperature appears to have risen by 0.7°C from the past 2000 year mean to 2004. This swamps the medieval warm period (0.3°C warmer) and the Little Ice Age (0.3°C cooler). Neither of these periods would been identified if the actual temp in a particular place had changed by only 0.3°C.

These periods saw far greater localised changes, including droughts, famines, removal of and re-establishment of Atlantic pack ice, and growth and abandonment of Viking settlements in Greenland and Newfoundland. If that is what 0.3°C fluctuations can do, a rise of 1.2°C from now, totalling a 1.9°C rise from the past 2000 year mean, is likely to be more severe.

Why haven't we seen these changes yet? I don't know that we haven't. Most likely the changes so far are brushed off as being random variations, but there SEEMS to be a large amount of small pieces of evidence for change. Extreme hot-Summer and cold-Winter weather in Europe, increasing anoxia in the Gulf of Mexico (due in part to pollution but also due to water temp rise), increases in flash floods, generally strengthening El Nino cycles, retreating glaciers, breakup of Antarctic ice shelves and measurable rise in sea level. I don't know how long it takes for the Earth to respond to temp rises, but I can't conclude it's not already happening.

We use oil for many things, not just transport. Many power stations are oil- and gas-fired. And as these decline, without a change in approach, coal is very likely to take over. Even if we switch to H2 or direct electric drive for vehicle power, these both require power generation, and that could well be from coal which could last hundreds of years more.

Temperature of Planet Earth. Fergus, 2008
The -11°C to +3°C variations you see at Vostok (I see -9°C to +3°C, but whatever) correspond to 3°C swings in mean global temp These global swings correspond to ice age glaciations which saw half of Europe, (including the UK and Switzerland) under ice kilometres thick. In the last 100 years we have changed the global temperature by half that already, and there is little sign of it failing to continue.

On that basis, personally I think a further 1.2°C rise, on top of the 0.7°C rise which appears already to have taken place, is anything but underwhelming.

That's why I think digging into the science is not only justified, but a responsibility for a thinking consumer. Even if that's not the way for churches or newspapers! Not everyone needs to agree on the conclusion, but I would not sleep well if I didn't make the effort to understand enough to justify the conclusion I've come to. But what to do about it......? I don't know where to start on that one!

Harvey: Your latest graph shows a span in temp over the past 2000 years of circa 1.2°C, a time that has been relatively unremarkable in terms of climate. Truly underwhelming as a threat to threat to civilization.

Billy: I wouldn't call differences between fully developed agriculture in Greenland during the Medieval Warm Period, and annual festivals on the frozen Thames in the Little Ice Age unremarkable, and that was during the period when the range was 0.8°C at most. The increase to 1.2°C has been in the last few decades, and I don't know what lag to expect between rises in mean temp and changes in climate behaviour.

Atmospheric CO2. Mauna Loa, Hawaii
While I think there is good reason to expect substantial effects from the 30% increase in CO2 we've undoubtedly caused already, I do depart from the 'end-of-the-world' extremists, and the laughably gullible 'day after tomorrow' panickers. Millions may die, nations may revolt, wars may be fought, islands may be inundated, species may become extinct, but mankind will survive and thrive in adversity just as it did through previous ice ages. We're as good at adapting as rats are!

Harvey: And here we converge! Thanks, that was fun...

Billy: Knew we'd get there in the end. :-)

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