Tag Archives: CO2

MondayMap: The Double Edge of Climate Change

So the changing global climate will imperil our coasts, flood low-lying lands, fuel more droughts, increase weather extremes, and generally make the planet more toasty. But, a new study — for the first time — links increasing levels of CO2 to an increase in global vegetation. Perhaps this portends our eventual fate — ceding the Earth back to the plants — unless humans make some drastic behavioral changes.

From the New Scientist:

The planet is getting lusher, and we are responsible. Carbon dioxide generated by human activity is stimulating photosynthesis and causing a beneficial greening of the Earth’s surface.

For the first time, researchers claim to have shown that the increase in plant cover is due to this “CO2 fertilisation effect” rather than other causes. However, it remains unclear whether the effect can counter any negative consequences of global warming, such as the spread of deserts.

Recent satellite studies have shown that the planet is harbouring more vegetation overall, but pinning down the cause has been difficult. Factors such as higher temperatures, extra rainfall, and an increase in atmospheric CO2 – which helps plants use water more efficiently – could all be boosting vegetation.

To home in on the effect of CO2, Randall Donohue of Australia’s national research institute, the CSIRO in Canberra, monitored vegetation at the edges of deserts in Australia, southern Africa, the US Southwest, North Africa, the Middle East and central Asia. These are regions where there is ample warmth and sunlight, but only just enough rainfall for vegetation to grow, so any change in plant cover must be the result of a change in rainfall patterns or CO2 levels, or both.

If CO2 levels were constant, then the amount of vegetation per unit of rainfall ought to be constant, too. However, the team found that this figure rose by 11 per cent in these areas between 1982 and 2010, mirroring the rise in CO2 (Geophysical Research Letters, doi.org/mqx). Donohue says this lends “strong support” to the idea that CO2 fertilisation drove the greening.

Climate change studies have predicted that many dry areas will get drier and that some deserts will expand. Donohue’s findings make this less certain.

However, the greening effect may not apply to the world’s driest regions. Beth Newingham of the University of Idaho, Moscow, recently published the result of a 10-year experiment involving a greenhouse set up in the Mojave desert of Nevada. She found “no sustained increase in biomass” when extra CO2 was pumped into the greenhouse. “You cannot assume that all these deserts respond the same,” she says. “Enough water needs to be present for the plants to respond at all.”

The extra plant growth could have knock-on effects on climate, Donohue says, by increasing rainfall, affecting river flows and changing the likelihood of wildfires. It will also absorb more CO2 from the air, potentially damping down global warming but also limiting the CO2 fertilisation effect itself.

Read the entire article here.

Image: Global vegetation mapped: Normalized Difference Vegetation Index (NDVI) from Nov. 1, 2007, to Dec. 1, 2007, during autumn in the Northern Hemisphere. This monthly average is based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. The greenness values depict vegetation density; higher values (dark greens) show land areas with plenty of leafy green vegetation, such as the Amazon Rainforest. Lower values (beige to white) show areas with little or no vegetation, including sand seas and Arctic areas. Areas with moderate amounts of vegetation are pale green. Land areas with no data appear gray, and water appears blue. Courtesy of NASA.

More CO2 is Good, Right?

Yesterday, May 10, 2013, scientists published new measures of atmospheric carbon dioxide (CO2). For the first time in human history CO2 levels reached an average of 400 parts per million (ppm). This is particularly troubling since CO2 has long been known as the most potent heat trapping component of the atmosphere. The sobering milestone was recorded from the Mauna Loa Observatory in Hawaii — monitoring has been underway at the site since the mid-1950s.

This has many climate scientists re-doubling their efforts to warn of the consequences of climate change, which is believed to be driven by human activity and specifically the generation of atmospheric CO2 in ever increasing quantities. But not to be outdone, the venerable Wall Street Journal — seldom known for its well-reasoned scientific journalism — chimed in with an op-ed on the subject. According to the WSJ we have nothing to worry about because increased levels of CO2 are good for certain crops and the Earth had historically much higher levels of CO2 (though pre-humanity).

Ashutosh Jogalekar over at The Curious Wavefunction dissects the WSJ article line by line:

Since we were discussing the differences between climate change “skeptics” and “deniers” (or “denialists”, whatever you want to call them) the other day this piece is timely. The Wall Street Journal is not exactly known for reasoned discussion of climate change, but this Op-Ed piece may set a new standard even for its own naysayers and skeptics. It’s a piece by William Happer and Harrison Schmitt that’s so one-sided, sparse on detail, misleading and ultimately pointless that I am wondering if it’s a spoof.

Happer and Schmitt’s thesis can be summed up in one line: More CO2 in the atmosphere is a good thing because it’s good for one particular type of crop plant. That’s basically it. No discussion of the downsides, not even a pretense of a balanced perspective. Unfortunately it’s not hard to classify their piece as a denialist article because it conforms to some of the classic features of denial; it’s entirely one sided, it’s very short on detail, it does a poor job even with the little details that it does present and it simply ignores the massive amount of research done on the topic. In short it’s grossly misleading.

First of all Happer and Schmitt simply dismiss any connection that might exist between CO2 levels and rising temperatures, in the process consigning a fair amount of basic physics and chemistry to the dustbin. There are no references and no actual discussion of why they don’t believe there’s a connection. That’s a shoddy start to put it mildly; you would expect a legitimate skeptic to start with some actual evidence and references. Most of the article after that consists of a discussion of the differences between so-called C3 plants (like rice) and C4 plants (like corn and sugarcane). This is standard stuff found in college biochemistry textbooks, nothing revealing here. But Happer and Schmitt leverage a fundamental difference between the two – the fact that C4 plants can utilize CO2 more efficiently than C3 plants under certain conditions – into an argument for increasing CO2 levels in the atmosphere.

This of course completely ignores all the other potentially catastrophic effects that CO2 could have on agriculture, climate, biodiversity etc. You don’t even have to be a big believer in climate change to realize that focusing on only a single effect of a parameter on a complicated system is just bad science. Happer and Schmitt’s argument is akin to the argument that everyone should get themselves addicted to meth because one of meth’s effects is euphoria. So ramping up meth consumption will make everyone feel happier, right?

But even if you consider that extremely narrowly defined effect of CO2 on C3 and C4 plants, there’s still a problem. What’s interesting is that the argument has been countered by Matt Ridley in the pages of this very publication:

But it is not quite that simple. Surprisingly, the C4 strategy first became common in the repeated ice ages that began about four million years ago. This was because the ice ages were a very dry time in the tropics and carbon-dioxide levels were very low—about half today’s levels. C4 plants are better at scavenging carbon dioxide (the source of carbon for sugars) from the air and waste much less water doing so. In each glacial cold spell, forests gave way to seasonal grasslands on a huge scale. Only about 4% of plant species use C4, but nearly half of all grasses do, and grasses are among the newest kids on the ecological block.

So whereas rising temperatures benefit C4, rising carbon-dioxide levels do not. In fact, C3 plants get a greater boost from high carbon dioxide levels than C4. Nearly 500 separate experiments confirm that if carbon-dioxide levels roughly double from preindustrial levels, rice and wheat yields will be on average 36% and 33% higher, while corn yields will increase by only 24%.

So no, the situation is more subtle than the authors think. In fact I am surprised that, given that C4 plants actually do grow better at higher temperatures, Happer and Schmitt missed an opportunity for making the case for a warmer planet. In any case, there’s a big difference between improving yields of C4 plants under controlled greenhouse conditions and expecting these yields to improve without affecting other components of the ecosystem by doing a giant planetary experiment.

Read the entire article after the jump.

Image courtesy of Sierra Club.


A Plan to Keep Carbon in Check

[div class=attrib]By Robert H. Socolow and Stephen W. Pacala, From Scientific American:[end-div]

Getting a grip on greenhouse gases is daunting but doable. The technologies already exist. But there is no time to lose.

Retreating glaciers, stronger hurricanes, hotter summers, thinner polar bears: the ominous harbingers of global warming are driving companies and governments to work toward an unprecedented change in the historical pattern of fossil-fuel use. Faster and faster, year after year for two centuries, human beings have been transferring carbon to the atmosphere from below the surface of the earth. Today the world’s coal, oil and natural gas industries dig up and pump out about seven billion tons of carbon a year, and society burns nearly all of it, releasing carbon dioxide (CO2). Ever more people are convinced that prudence dictates a reversal of the present course of rising CO2 emissions.

The boundary separating the truly dangerous consequences of emissions from the merely unwise is probably located near (but below) a doubling of the concentration of CO2 that was in the atmosphere in the 18th century, before the Industrial Revolution began. Every increase in concentration carries new risks, but avoiding that danger zone would reduce the likelihood of triggering major, irreversible climate changes, such as the disappearance of the Greenland ice cap. Two years ago the two of us provided a simple framework to relate future CO2 emissions to this goal.

[div class=attrib]More from theSource here.[end-div]