Wednesday, July 18, 2012

Graphs can be terrifying: Getting a grip on CO2

H/T Gareth.
This soundless little presentation from NOAA's Carbon Tracker shows atmospheric carbon dioxide (CO2) concentrations over time. The first half of the video shows on the left hand side the yearly rise and fall of CO2 concentrations around the world since 1979. The various dots along the line each represent a different location around the globe, arranged by latitude, with the blue dot on the far left being the south pole and the dots at far right representing measurements in the Arctic. The dots rise and fall in a regular pattern as time passes. This is because trees "breathe in" CO2 during the northern spring/summer as leaves photosynthesise and then "breathe out" in autumn/winter as leaves decay, meaning that atmospheric concentrations rise and fall a little each year in a natural cycle. The annual variations are far more pronounced in the north hemisphere (the right end of the line that bounces up and down) since there is a much greater mass of land (and so trees) up here than in the southern hemisphere. So the concentration is never exactly the same at every point in the world or on every day of the year. And yet, along with the annual cycle there is something else happening. The overall movement is unmistakeable: up, up, up. If we look at the right hand side of the display, which shows the famous "Keeling curve" of average CO2 concentrations going back to 1958 when precise records first began to be kept (by Prof C. D. Keeling at Moana Loa in Hawaii), we can see that the annual rise and fall of the natural carbon cycle is superimposed on and ultimately dwarfed by a relentless upwards rise, which represents the human contribution to the situation. Each year we dig up literally billions of tonnes of carbon that had been safely stored for millions of years underground and burn it to power our lightbulbs and laptops, our concrete and cars, our fridges and flights.

Once the period 1979-2011 has been shown (up to about 1:40 in the video), we begin to zoom out, seeing further back in time. Initially, we are introduced to the earlier progress of the Keeling curve as it wobbles up and down back to 1958 (the green part of the cuve, spanning roughly 1:40-2:00 in the video). Then we suddenly begin zooming out much more quickly, and the green curve becomes a series of yellow dots spanning back to the time of Christ (2:00-2:20). Since the apostles were not measuring CO2, these measurements are "proxies", reconstructions of historical concentrations from a wide range of sources that have preserved a natural record of atmospheric concentrations. From 2:20-3:00, the blue curve represents a record of pre-historic CO2 concentrations going back 800,000 years (ka = thousand years; BCE = Before Common Era = BC) preserved in the ancient sheets of Greenland and Antarctica (Antarctica has the deepest ice and so the oldest records). The line here jumps up and down over many thousands of years as the world went into and out of glaciations (commonly, though incorrectly, known as "ice ages"). When CO2 concentrations were low (below 200 ppm), huge sheets of ice covered vast areas of land in the northern hemisphere. We have very good reasons for believing that CO2 concentrations played a crucial (though not exclusive) role in previous natural changes in climate.

The units used to measure CO2 concentrations are parts per million (ppm), that is, the the y-axis (vertical axis) represents the number for CO2 molecules for every million molecules of gas in the atmosphere, so 300 ppm means 0.03% of the atmosphere was CO2. These seem like tiny amounts and it is true that CO2 is a trace gas, but the effects of even small changes in some trace elements can be very large. If we were adding arsenic to a cup of coffee, then a mere 300 ppm would be sufficient to kill you. So don't be fooled by those who point to the "small" numbers involved. Changing the CO2 concentration from 280 ppm (as it was prior to the Industrial Revolution) to today's level of approximately 395 ppm represents the addition of more than a trillion tonnes of carbon dioxide.

So what does this all mean? This presentation very usefully shows the very large natural atmospheric changes in the earth's "recent" experience (recent by geological standards, since the earth itself is 4.5 billion years old). Notice that the difference between glaciers thousands of metres thick covering most of the UK and more temperate periods during which life can flourish on these isles was only about 100 parts per million.

Human agriculturally-based civilisation has only existed in the most recent 10,000 years (known as the "Holocene"), during which time CO2 concentrations (and so climate) have been fairly stable. Or had been.

So what we see (or is at least hinted at) in this video is (a) the ability of relatively "small" changes in a trace gas like CO2 to produce huge, world-changing effects on climate, (b) the relative stability (CO2 and climate-wise) of the period during which human civilisation has developed and (c) the dramatic and very sudden jump in CO2 concentrations during the last 150 years or so, accelerating rapidly over the last six decades. Compared to all previous changes, the rate of change we're seeing is off the charts. In comparison to even the steepest rises and falls during glaciations and de-glaciations, the last century or so has been basically a vertical rise, almost the equivalent of a de-glaciation in the blink of an eye. And we're already in uncharted waters, at concentrations not seen for at least 800,000 years (indeed other proxies that go back even further - albeit with lower levels of confidence - suggest that CO2 concentrations have not been this high for at least 20 million years). And if you look at the numbers on the y-axis, keep in mind that our current trajectory, in the absence of either global economic collapse or a massive energy and/or cultural revolution, will take us above 800, 900 or even 1,000 ppm during my daughter's expected lifetime. We ain't seen nothing yet.

And carbon, once removed from the stability and safety of underground storage, sticks around in the oceans, atmosphere and soils (the "active carbon cycle") for a very long time. We'll see elevated levels of carbon for hundreds and even thousands of years after we reduce human emissions to zero. It's important to keep clear in your mind the difference between emissions and concentrations. Emissions are like income going into your bank account, concentrations are like your account balance. So if we get to a concentration of, say, 700 ppm and decide to go on a crash diet of zero emissions, things won't return to "normal" for tens of thousands of years.
One recent study pointed out that CO2 released by pre-industrial deforestation continues to affect climate today, albeit on nothing like the scale of industrial activities.

Why is this a problem? Many serious and senior researchers believe that life as we know it is incompatible with CO2 concentrations above 450 ppm. In the long run, many think that anything over 350 ppm is too high since 450 ppm could well trigger the extinction of literally millions of species, perhaps a third of all those currently on the planet. Remember, we're currently at about 395 ppm and rising by more than 2 ppm each year.

Yet the insidious thing is that the effects of elevated CO2 concentrations are not immediately apparent. It can take decades for global temperatures to respond to shifts in atmospheric composition, centuries before the full effects are visible and millennia before sea levels will stabilise. So that means the crazy shifts we're already seeing are merely the result of where CO2 concentrations had reached back in about 1980 or so. Even with the best efforts, things are going to get worse for some time after we start taking this problem seriously. Thus any generation that chooses to forgo the seductive and wondrous benefits of fossil fuels will not immediately reap the rewards. We can always kick the can down the road for a few more years, but in doing so, we condemn our children (and their children and as many generation as we can imagine) to an increasingly hellish existence.


Anonymous said...

"Graphs can be terrifying: Getting a grip on CO2... This soundless little presentation from NOAA's Carbon Tracker shows atmospheric carbon dioxide (CO2) concentrations over time."

It's actually a little more terrifying if you add a little sound. ;)

byron smith said...

Thanks! That soundtrack is actually quite appropriate: a repetitive building menace with occasional bursts of change into greater drama. Since your version has been slightly compressed/speeded up to fit the soundtrack, the time references in my post don't quite work.

And your version, for some reason, only includes data going to 2008. Perhaps it is because your version was posted earlier, being posted in Feb 2011, while mine is from Sept 2011.

Though I'm very tempted to switch videos, I think I'll stick with the silent horror movie for the moment, allowing the soundtrack to be merely the sound of our own breath, rising and falling.

byron smith said...

SkSci: How do we know elevated CO2 levels are anthropogenic? Ten lines of evidence.

Unknown said...

Is there much effort going into reforestation on a massive global level, more that anti-logging campaigns? What would it take to turn the Sahara into a rainforest of a couple of centuries? With our knowledge of global weather patterns would it be possible to target areas of land and vegetate it to stop the hot dry winds developing that cause desertification. We could then incrementally increase the vegetation over time.

byron smith said...

Hi Aaran, welcome to commenting here.

There is indeed.

China has already begun the world's largest reforestation programme, which has put a significant dent in the net global forest cover loss over the last decade, but there are some major questions about the way it is being done.

And in Africa, there is the Great Green Wall project, which after 20 years of talk, finally got a little funding earlier this year.

As important as these measures are, they remain only a fraction of the scale of deforestation (albeit not a tiny one). And forest replaced is not nearly as valuable from either a carbon or biodiversity perspective (nor an economic perspective) as old growth forest.

Finally, it's also worth pointing out that putting more carbon back into biomass (i.e. the wood of trees in a forest - a fair chunk also goes into the soil) is only a short to medium term response, since one of the likely effects of a changing climate is to shift much or even most of the planet's surface from one biome to another. So much of the Amazon, for instance, could well turn into savannah after a few more degrees warming. This highlights the fact that carbon in biomass is still in the active carbon cycle, and can quite thinkably end up back in the atmosphere and oceans. It has not been safely stored away, merely put on hold for what may end up amounting only to a few decades. The only really safe place for excess carbon is underground, stored as fossil hydrocarbons. We simply have to leave the vast majority of these where they are and not dig them up and burn them.

byron smith said...

PhysOrg: Last time CO2 levels were this high .

"The last time carbon dioxide levels were apparently as high as they are today — and were sustained at those levels — global temperatures were 5 to 10 degrees Fahrenheit (2.8-5.6ºC) higher than they are today, the sea level was approximately 75 to 120 feet (22.9-36.6m) higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland".