Tag: Global Science Report

CO2 Benefits Outweigh Climate Stressors: Chinese Wheat

Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

In the vast majority of laboratory and field experiments, the benefits of higher atmospheric carbon dioxide (CO2) concentrations for plants (including food crops) generally outweigh the negative impacts from climate change. And this is even assuming the “dumb farmer scenario” that we recently blogged, in which farmers and agronomists don’t develop new production techniques, technologies, crop varietals, etc., to adapt to change, turning expected losses into gains. There is overwhelming evidence such as the remarkably robust increase that has occurred in the yield of most of the world’s major crops when grown in developing or developed nations. In other words, adding CO2 to the atmosphere may be a win-win situation for the world’s vegetation, but we digress…

Here, we’ll highlight a new study showing that including the fertilization effect of higher CO2 concentrations in a crop model of wheat grown in China turns projections of future climate change-driven reductions in crop yields into CO2-driven yield increases.

The study was conducted by researchers Yujie Liu and Fulu Tao of the Chinese Academy of Sciences and will soon be published in the Journal of Applied Meteorology and Climatology. Liu and Tao used a complex crop model to evaluate the changes in wheat production (which accounts from 22% China’s primary food production), in the main wheat cultivation areas in China under three climate change scenarios—global temperature increases of 1°, 2°, and 3°C. They modeled the crop response both with and without considering the fertilization impacts of additional atmospheric CO2 concentrations (which presumably produced the warming) and compared the results. Here is their summary:

There is a high probability of decreasing (increasing) changes in yield and water use efficiency under higher temperature scenarios without (with) consideration of CO2  fertilization effects. Elevated CO2 concentration generally compensates for the negative effects of warming temperatures on production. Moreover, positive effects of elevated CO2 concentration on grain yield increase with warming temperatures. The findings could be critical for climate change-driven agricultural production that ensures global food security.

Findings and conclusions like these are a breath of carbon dioxide-enhanced fresh air in a world of climate gloomsaying.

Reference:

Liu, Y., and F. Tao, 2012. Probabilistic change of wheat productivity and water use in China for global mean temperature changes of 1, 2, and 3°C. Journal of Applied Meteorology and Climatology, doi:10.1175/JAMC-D-12-039.1, in press.

The Latest Greenland Kerfluffle: If Their Science Can’t Be Refuted, Smear ‘Em

Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

About a year and a half ago, we were co-authors (along with Dr. Oliver Frauenfeld from Texas A&M University) on a paper published in the Journal of Geophysical Research in which we presented a nearly 225-year reconstruction of surface snow melt across Greenland (Figure 1).

Our reconstruction was based on long-term temperature records from the southern Greenland coast along with historic indicators of the atmospheric circulation in the North Atlantic Ocean. We found that in addition to the period since about the year 2000, there was an extended (multi-decadal) period in the early portion of the 20th century where the amount of surface snowmelt was elevated above the long-term average.  We concluded from this that since there did not appear to be a large increase in the rate of global sea level rise during the early 20th century period of elevated ice melt—a melt driven primarily by warmer than normal temperatures—that Greenland’s contribution to global sea level rise during the current period of high temperatures was likely to remain relatively “modest,” at least for the next few decades.

Figure 1. Reconstructed history of the total ice melt extent index over Greenland, 1784–2009. Observed values of the ice melt index (blue solid circles), reconstructed values of the ice melt index (gray open circles), the 10 year trailing moving average through the reconstructed and fitted values (thick red line), and the 95% upper and lower confidence bounds (thin gray lines) (from Frauenfeld et al., 2011).

Neither our methods, nor or findings were overly controversial—or so we thought.

Shortly after our paper was published, one of the reviewers of our paper, a noted snow/ice researcher who has spent a lot of time studying Greenland, Dr. Jason Box, came forwarded and denounced our work. On his blog (in posts he has subsequently removed), he attacked our work both from a scientific standpoint as well as deriding it with a few ad hominems (for example “Examining the 2nd [Knappenberger] and 3rd [Michaels] authors’ credentials, a climate change denialist pattern emerges”).

On both accounts we felt he was wrong (of course) and offered a rebuttal.

But perhaps the strongest argument that our results were scientifically sound comes from an ironic source—the results of new research findings from Jason Box himself!

These new findings from Box, although not yet fully available, have been incorporated into another research project that has recently been published (Gregory et al., 2012) and thus we can get a sneak peek at them.

The solid black line in Figure 2 (below) shows Box’s reconstruction of the sea level rise contribution from Greenland back into since the mid-1800s.

Figure 2. Various estimates of the time series of the Greenland ice-sheet mass contribution to global-mean sea-level rise. The reconstructions are plotted as ten-year running time-means of the sea-level equivalent of the rate of change of mass of the Greenland ice-sheet with respect to the mean of 1961–1990. The solid black line, labeled “B” is the net mass balance, including both surface mass balance and ice discharge from Jason Box. The horizontal dotted line indicates zero. The vertical lines indicate the years in which major volcanic eruptions occurred (from Gregory et al., 2012).

Notice the strong resemblance of Box’s reconstruction of the sea level contribution from Greenland with our reconstruction of the surface snow melt across Greenland.  The snow melt/sea level contribution is currently very high, was relatively low in the 1970s, 1980s, and 1990s, was high from the mid-1920s through the late 1960s, and was lower in the 1800s.

Considering that there are other factors besides snowmelt (like snow accumulation and calving glaciers) that contribute to Greenland’s net contributions to sea level rise, the two curves are remarkably similar. This is a strong indication that whatever is driving snowmelt (regional temperature) is also driving the net sea level contribution.

All of which we wrote in our paper:

This record of ice melt indicates that the melt extent observed since the late 1990s is among the highest likely to have occurred since the late 18th century, although recent values are not statistically different from those common during the period 1923–1961, a period when summer temperatures along the southern coast of Greenland were similarly high as those experienced in recent years. Our reconstruction indicates that if the current trend toward increasing melt extent continues, total melt across the Greenland ice sheet will exceed historic values of the past two and a quarter centuries

…The forces acting in concert with ice melt across Greenland to produce higher global sea levels currently, should also have been acting during the extended high‐melt conditions from the mid‐1920s to the early 1960s.

And we also added this concerning the significance of Greenland’s contribution to the total global sea level rise:

[T]here is no indication that the increased contribution from the Greenland melt in the early to mid 20th century, a roughly 40 year interval when average annual melt was more or less equivalent to the average of the most recent 10 years (2000–2009), resulted in a rate of global sea level rise that exceeded ~mm/yr.  This suggests that Greenland’s contribution to global sea level rise, even during multidecadal conditions as warm as during the past several years, is relatively modest.

Figure 3 (anther figure from the new paper from Gregory et al., 2012) shows the breakdown of the factors contributing to the global rise in sea level of the past century and a half.  Greenland’s contribution (based on Box’s reconstruction) is the pale green line (labeled “Greenland-B” in the legend). I think it is pretty fair to characterize this as “modest.”

Figure 3. Observational (black) and a reconstructed (red) time series of global mean sea-level rise (thick lines, with 5–95% observational uncertainty shaded), also showing the contributions to the latter (thin lines), identified by the time series initials in the key (from Gregory et al., 2012).

Why was such a big deal was made about our research results and “denialist” credentials when subsequent results, made by the very person who went ad hominem, completely replicate our findings?

References:

Box, J. E., Greenland ice sheet mass balance reconstruction. Part III: Marine ice loss and total mass balance (1840–2010). Journal of Climate, submitted (as cited by Gregory et al., 2012).

Frauenfeld, O.W., P.C. Knappenberger, and P.J. Michaels, 2011. A reconstruction of annual Greenland ice melt extent, 1785-2009. Journal of Geophysical Research, 116, D08104, doi: 10.1029/2010JD014918.

Gregory, J., et al., 2012. Twentieth-century global-mean sea-level rise: is the whole greater than the sum of the parts? Journal of Climate, doi:10.1175/JCLI-D-12-00319.1, in press.

Climate Sensitivity Going Down

Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

“Climate sensitivity” is the amount that the average global surface temperature will rise, given a doubling of the concentration of atmospheric carbon dioxide (CO2) in the atmosphere from its pre-industrial value. This metric is the key to understanding how much global warming will occur as we continue to burn fossil fuels for energy and emit the resultant CO2 into the atmosphere.

The problem is that we don’t know what the value of the climate sensitivity really is.

In its Fourth Assessment Report, released in 2007, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) had this to say about the climate sensitivity:

It is likely to be in the range 2°C to 4.5°C with a best estimate of about 3.0°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded…

In IPCC parlance, the term “likely” means a probability of greater than 66% and “very likely” means a greater than 90% change of occurrence. The IPCC’s 90% range for the climate sensitivity  includes values at the low end which, if proven true, would engender very little concern over our use of fossil fuels as a primary energy source, and values at the high end would generate calls for frantic efforts (which would likely fail)  to lower carbon dioxide emissions.

While there has been a lot of effort expended to better constrain estimates of sensitivity over the past several decades, little progress has been made in narrowing the range.  The IPCC’s First Assessment Report, released back in 1990, gave a range of 1.5°C to 4.5°C.  It’s not that climate science hasn’t progressed since then, but just that the advanced understanding has not led to substantially better constraints.

But what has occurred over the past several decades is that greenhouse emissions have continued to rise (in fact, half of the total anthropogenerated  carbon dioxide emissions have been since the mid-1980s), and global temperature observations have continued to be collected.  We now have much more data with which to use to try to determine the sensitivity.

While global carbon dioxide emissions continue to rise year-over-year (primarily driven by the rapid growth in developing countries such as China), global temperatures have not kept up—in fact, there has been little to no overall global temperature increase (depending upon the record used) over the past decade and a half.

That doesn’t bode well for the IPCC’s high-end temperature sensitivity estimates. The scientific literature is now starting to reflect that reality.

Never mind that Pat Michaels and I published a paper in 2002 showing that the sensitivity lies near the low side of the IPCC’s range.  This idea (and those in similar papers subsequently published by others) had largely been ignored by the “mainstream” scientists self-selected to produce the IPCC Assessments.  But new results supporting lower and tighter estimates of the climate sensitivity are now appearing with regularity,  a testament to just how strong the evidence has become, for such results had to overcome the guardians of the IPCC’s so called “consensus of scientists”, which the Climategate emails showed to be less than gentlemanly.

Figure 1 shows the estimates of the climate sensitivity from five research papers that have appeared in the past two years, including the recent contributions from Ring et al. (2012) and van Hateren (2012)—both of which put the central estimate of the climate sensitivity at 2°C or lower, values which are at or beneath the IPCC’s  current “likely” range.

Figure 1. Climate sensitivity estimates from new research published in the past two years (colored), compared with the range given in the IPCC Fourth Assessment Report (black). The arrows indicate the 5 to 95% confidence bounds for each estimate along with the mean (vertical line) where available. Ring et al. (2012) present four estimates of the climate sensitivity and the red box encompasses those estimates.  The right-hand side of the IPCC range is dotted to indicate that the IPCC does not actually state the value for the upper 95% confidence bound of their estimate. The thick gray line represents the IPCC’s “likely” range.

The IPCC is scheduled to release its Fifth Assessment Report in 2013.  We’ll see whether these new, lower, and more constrained estimates of climate sensitivity  that are increasing populating the literature result in a modification of the IPCC estimates, or whether the IPCC authors manage to wave  them all away (or simply ignore them, as was the case with our 2002 paper).

Regardless of how the IPCC ultimately assesses climate science in 2013, the fact of the matter is that there is growing evidence that anthropogenic climate change from the burning of fossil fuels is not going to turn out to be as much as climate alarmists have made it out to be.

References:

Annan, J.D., and J.C. Hargreaves, 2011. On the genera­tion and interpretation of probabilistic estimates of climate sensitivity. Climatic Change, 104, 324-436.

Lindzen, R.S., and Y-S. Choi, 2011. On the observational determination of climate sensitivity and its implica­tions. Asia-Pacific Journal of Atmospheric Sciences, 47, 377-390.

Michaels, P.J., P.C. Knappenberger, O.W. Frauenfeld, and R.E. Davis, 2002. Revised 21st century temperature predictions. Climate Research, 23, 1-9.

Ring, M.J., et al., 2012. Causes of the global warming observed since the 19th century. Atmospheric and Climate Sciences, 2, 401-415, doi:10.4236/acs.2012.24035.

Schmittner, A., et al., 2011. Climate sensitivity estimat­ed from temperature reconstructions of the Last Glacial Maximum, Science, 334, 1385-1388, doi: 10.1126/science.1203513.

Solomon, S., et al., (eds.), 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, 996pp.

van Hateren, J.H., 2012. A fractal climate response function can simulate global average temperature trends of the modern era and the past millennium. Climate Dynamics, doi:10.1007/s00382-012-1375-3.

Straw Men

Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

Lawrence Livermore National Laboratory’s Benjamin Santer and his mentor, Tom Wigley, of the National Center for Atmospheric Research seem, well, a little obsessed over Cato’s Pat Michaels.  First, Santer threatened to “beat the cr&p out of him”, and then Wigley tried to foment a cabal to “re-assess” his doctoral dissertation, under grounds that were completely, unalterably, and demonstrably 100 percent false.

So it’s no surprise that they have just published—two years after the fact—what they consider to be a rejoinder to Michaels’ 2010 testimony to the Subcommittee on Energy and Environment of the Committee on Science and Technology of the United States House of Representatives.  There’s about as much real substance here as there was in Wigley’s very ill-informed (and seemingly actionable, if Michaels didn’t have a day job here at Cato) campaign against his doctorate.

It’s just been published in the journal Climate Dynamics.  This is technically peer-reviewed, but, judging from the climategate emails and the serial paper trail of threatening journal editors (say, by writing to the University administrations where they worked) as well as the less than high quality contents of the actual paper, it makes you wonder just how critical the reviewers actually were.

In their paper, Wigley and Santer wrote:

Michaels’ 2010 Congressional testimony…is in conflict with the results presented here. This testimony makes the claims that “…greenhouse-related warming is clearly below the mean of relevant forecasts by IPCC”, and that “… the Finding of Endangerment from greenhouse gases by the Environmental Protection Agency is based on a very dubious and critical assumption”. The “assumption” referred to here is the IPCC statement that is the primary focus of the present paper, i.e., the statement that most of the warming since 1950 is very likely due to the human-caused increase in greenhouse gas concentrations.

Regarding Michaels’ statement that “…greenhouse-related warming is clearly below the mean of relevant forecasts by IPCC” Wigley and Santer argued that:

Roughly half of these [IPCC climate model] simulations did not consider the cooling effect of indirect aerosol forcing, so the results, on average, would be biased towards trends that are warmer than observed even if the models were perfect (cf. Santer et al. 2011).

So the climate models are biased to producing more warming than is observed? Isn’t that what Michaels said? These guys just won’t take “yes” for an answer.

And in fact, the reference in the above quote to “Santer et al. 2011” is a paper published by Santer and Wigley (and 15 others) that finds:

The multi-model average [lower atmospheric temperature] trend is always larger than the average observed [lower atmospheric temperature] trend…[a]s the trend fitting period increases…average observed trends are increasingly more unusual with respect to the multi-model distribution of forced trends.

That says what you think it says! Model temperature trends are always higher than the observed temperature trends and that over longer periods (i.e., more robust analysis) the model/observed discrepancy grows. Here is the relevant figure from that paper.

Figure 1. A comparison between modeled and observed trends in the average temperature of the lower atmosphere, for periods ranging from 10 to 32 years (during the period 1979 through 2010). The yellow is the 5-95 percentile range of individual model projections, the green is the model average, the red and blue are the average of the observations, as compiled by Remote Sensing Systems and University of Alabama in Huntsville respectively (adapted from Santer et al., 2011).

Their own analysis supports Michaels’ contention, which they somehow say is wrong.  Beats me.

In fact, their picture looks an awful lot like the one that Michaels used in his testimony (Figure 2).

Figure 2. Range of climate model probabilities of surface temperature trends (gray shading) overlaid with the observed surface temperature trend from the Climate Research Unit (blue line) (data through September 2010).

It’s worth noting that Michaels’ was the first presenter of this type of chart several years ago.  In fact, Wigley reviewed a paper it was in, helped get the editor to kill it, and then, with Santer, published something mighty similar.  How strange for someone they are arguing is wrong.

It goes on.

They then take exception with Michaels’ statement to Congress that the IPCC’s central finding that “[m]ost of the observed increase in global average temperatures since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” is “dubious.”

Wigley and Santer spill a lot of ink over the concept that in the absence of everything else, that the potential warming from anthropogenic greenhouse gases is likely greater than the observed warming. Michaels didn’t say that it wasn’t. In fact, most people believe this as true.

Michaels was concerned about the observed warming not some hypothetical, unrealizable (and therefore unverifiable) change. After all, it is the actual warming that the environment largely responds to. So when assessing the accuracy of the IPCC statement on observed warming, it is therefore appropriate to divide it up between various elements as he did.

While there’s a lot of gory detail in this discussion (see here, for more ), one thing that I think we all should be able to agree on is that it is physically impossible for something (like the emissions of anthropogenic greenhouse gases) to be responsible for causing more than 100% of what has been observed, and that such statements like this one from Wigley and Santer’s paper,

Here, the probability that the model-estimated GHG component of warming is greater than the entire observed trend (i.e., not just greater than ‘‘most’’ of the observed warming) is about 93%.

is something other than science, because one surely cannot find something that nature will not reveal.

The bottom line here is that in their paper, Wigley and Santer seem to place more import on the attack of Pat Michaels, than they do on the actual logic behind it.


References:

Santer,  B. D., C. Mears, C. Doutriaux, P. Caldwell, P.J. Gleckler , T.M.L. Wigley, S. Solomon, N.P. Gillett, D. Ivanova D, T.R. Karl, J.R. Lanzante, G.A. Meehl, P.A. Stott, K.E. Taylor, P.W. Thorne, M.F. Wehner, F.J. Wentz, 2011. Separating signal and noise in atmospheric temperature changes: the importance of timescale. Journal of Geophysical Research116, D22105. doi:10.1029/2011JD016263

Wigley, T.M.L., and B.D. Santer, 2012. A probabilistic quantification of the anthropogenic component of twentieth century global warming. Climate Dynamics, doi: 10.1007/s00382-012-1585-8

Carbon Tax Follies

Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

There seems to be a noticeable murmur around town about a carbon tax—a tax on the amount of carbon dioxide that is released upon generating a unit of energy. Since fossil fuels—coal, oil, natural gas—are both the source of over 75% of our energy production and emitters of carbon dioxide when producing that energy, a carbon tax insures that the price of everything goes up.

There is one and only one justification for a carbon tax—an attempt to influence the future course of the earth’s climate (or, as some people prefer, to mitigate anthropogenic climate change) by trying to force down the emissions of the most abundant human-generated greenhouse gas.

But of all the things that a carbon tax will do (raise prices, increase bureaucracy, elect Tea Partiers, etc), mitigating anthropogenic climate change in any meaningful manner is not one of them.

The annual carbon dioxide emissions from the U.S., currently about 5,500 million metric tons per year, only contributes roughly 0.003°C/per year of warming pressure on global temperatures (see here for a handy way of making that calculation). So the best that a carbon tax could ever hope to achieve, climatically, would be to prevent this amount of warming each year by completely eliminating all carbon dioxide emissions from the U.S.

If we went to zero emissions tomorrow,  the carbon tax would prevent about 0.26°C of global temperature rise by the year 2100. According to the latest projections from the Intergovernmental Panel on Climate Change (IPCC), the projected temperature rise by the end of the century ranges from about 1.1 to 6.4°C, with a business-as-usual rise of around 3°C (put me down for 1.6° until then, unless nature is being a blatant liar).  The “mitigated” rise is proportional to the expected temperature rise. A carbon tax enacted today that is immediately and completely successful at eliminating all U.S. CO2 emission would lower rise in temperature expected by the end of the century around 10%.  This amount is small, of little consequence, and in fact will be difficult to detect.

It is also not going to happen.  We only have the capacity to produce about 30% of our electricity from non-carbon emitting fuel sources (primarily nuclear and hydroelectric). So it will take time, and probably a lot of time (many decades) before our energy needs could possibly be met without emitting CO2 into the atmosphere.  And of course, as time ticks by before eliminating or at least appreciably reducing  our emissions, the amount of global warming saved by such action declines (and become less and less consequential), as does the justification for the carbon tax.

I am just in the early stage of this analysis, so the numbers above are a bit rough (but conservative). In the future I hope to produce a menu of emissions reductions/climate savings options—but one without prices.  That way the policymakers will see what they are going to be getting for whatever price they decide to assign. So too will the general public. And what they will all see is that whatever level of carbon tax they decide upon,  they will get a lot of climate nothing  for a lot of financial something.

The best thing would be for policymakers to just leave well enough alone, for on their own, carbon dioxide emissions in the U.S. have been declining for more than a decade (and in fact are pushing levels of the early 1990s, http://www.eia.gov/environment/emissions/carbon/). And even if such a reduction doesn’t result in any scientifically detectable climate impacts, at least it hasn’t cost us anything.

Arguing over Sandy

Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

On Monday of this week, three prominent and influential scientists published an opinion piece in Politico arguing that anthropogenic global warming was responsible for making the destruction from “super storm” Sandy significantly worse than it otherwise would have been. They added that if we don’t “cut industrial carbon pollution,” we are going to get more of the same, and then some.

On the same day, I argued here at Cato@Liberty that it could be reasoned that anthropogenic global warming lessened the impact of Sandy.

The scientific truth about the situation is that it is impossible to know who is right—the uncertainties are just too large. But I think it is fair to say that no matter what direction the influence of anthropogenic global warming was on Sandy, in net it was quite small.

One difference between my piece and the Politico article co-signed by Dr. Robert Corell (“senior policy fellow for the American Meteorological Society and former Chair of the United States Global Change Research Program”), Dr. Jeff Masters (“the founder and Director of Meteorology for Weather Underground and a former NOAA Hurricane Hunter”) and Dr. Kevin Trenberth (“Distinguished Senior Scientist in the Climate Analysis Section at the National Center for Atmospheric Research”) was that I tried to stick to a scientifically defensible argument.  In their piece, they juiced up their case with some—how should I say this?—rather dubious facts.

The worst of these was claiming that “[o]n the stretch of the Atlantic Coast that spans from Norfolk to Boston, sea levels have been rising four times faster than the global average.” They implied that anthropogenic global warming was the reason why.

This is simply untrue.

While it is true that the long-term (~20th century) rate of sea level rise along that stretch has been about twice the global average over the same period, it is scientifically well-established that the regional enhanced rate of sea level rise is due to ongoing geologic processes resulting from end of the last ice age. When these non-anthropogenic processes are properly subtracted out of the tide gauge record of sea level observations, the rate of sea level rise that is left over is virtually the same as the global rate of rise, not four times faster.

The same conclusion is reached if you limit your comparison to the period of satellite observations of sea level, which began about 20 years ago.  The figure below shows a map of the satellite-measured trends in sea level from 1993 through mid-2012.  The global average rate of rise is 0.12 inches per year, which is represented by a sort of greenish yellow color.  Turning your attention to the Northeast coast of the United States (you might have to squint a bit), you see that the color there is also sort of greenish yellow—in other words, right about the global average.  Places where the sea level is rising four times faster than the global average are colored a light pink; while there are a few such places, none of them are anywhere near the stretch of coast between Norfolk and Boston.

Figure 1. Spatial distribution of the rate of sea level rise across the globe as measured by satellite altimeters (Source: University of Colorado Sea Level Group, modified to reflect English units).

It is somewhat telling when prominent climate scientists have to resort to incorporating incorrect (and readily debunked) science to try to bolster their case for climate alarm—an alarm that was raised to try to scare us into accepting regulations on greenhouse gas emissions.

New Evidence that Plants Are Slowing the Growth of Greenhouse Gases

Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

Scientists have known for decades that, as global carbon dioxide levels increase, so too does the standing biomass of the world’s plants. Carbon dioxide is a strong plant fertilizer.

As plants grow better, they also increasingly act as carbon sinks as they convert atmospheric carbon dioxide, with a little help from water and sunshine, into carbohydrates stored as biomass. Some of that carbon is returned to the air annually through decomposition, but other portions are are stored for longer periods in the soil, downed logs, houses, etc.  This plant-based carbon sink helps to offset the growth of global carbon dioxide emissions from human activities (primarily from the burning of fossil fuels). Together, the terrestrial carbon sink, along with the oceanic carbon sink, annually takes up more than half of the anthropogenic CO2 emissions—and remarkably, as global CO2 emissions have increased, so too has the global CO2 sink.

But now comes new evidence that plants may be helping to combat global warming through another mechanism as well, slowing the build-up of the atmospheric concentration of methane (a greenhouse gas some 25 times more effective than CO2 on a molecule-for-molecule bases at adding pressure for the world to warm).

As shown in the fugure below the jump, the growth rate of the atmospheric concentration of methane (CH4)—which is projected by the IPCC to be rising rapidly—began slowing down in the early 1990s and even topped out for a few years in the mid-2000s. Since about 2007, the atmospheric concentration of CH4 has been rising again, but only at about half that of the pre-1990 rate.

Figure 1. Atmospheric methane concentration (source: National Oceanic and Atmospheric Administration).
This behavior is not understood by climate scientists. It contravenes alarmist scenarios of runaway global warming fueled by a positive methane feedback (the scenario for which is that warming leads to thawing of the arctic permafrost, which releases methane, which leads to more warming, and so on).

A team of scientists from Lund University and Stockholm University set out to investigate recent claims that some plants release methane and are therefore a source of global methane emissions. They set up instruments to measure methane exchange on a collection of individual branches of four different tree species in a 100-year-old forest in central Sweden. A set of control experiments was also conducted in a laboratory setting. They just published their findings in the journal Geophysical Research Letters. Much to their surprise, the researchers found that the trees (both in the field and in the lab) were taking up methane rather than releasing it. They suggest that the presence of a “bacteria with the ability to consume [methane] would be a possible explanation for [the observed behavior].”

That’s not the only good news.

The researchers then executed the extremely risky (and oft ill-advised) maneuver of scaling up from a few tree branches in central Sweden to the level of the global forest canopy. Their research “indicates that the canopy might play an equally important role [in CH4 uptake] as the soil in the global context.” In other words, their results show that trees are playing a large (and hitherto unknown) role as a sink in the global methane cycle.

The culprit?  Increasing atmospheric carbon dioxide.

In the authors’ own words (with my emphasis):

Two recent studies give alternative explanations to the slow-down in the growth rate of atmospheric methane in the last decades. One of them indicates that it is due to a stabilization of fossil-fuel emissions (Aydin et al., 2011) whereas the other explains it by a decrease in microbial methane sources in the northern hemisphere (Kai et al., 2011). Our results offer a third explanation: that an increasing amount of CH4 has been taken up by vegetation during the last decades as a consequence of increased greenness (Myneni et al., 1997), NPP [net primary production] (Nemani et al., 2003) and GPP [gross primary production] (Chen et al., 2006) as observed by satellite remote sensing.

This is still highly a highly speculative result and one that will require a heck of a lot more study and independent confirmation. But it is a novel finding and goes to show that there is still a lot of interesting research ongoing in the field of climate (change), and that most definitely the science is not “settled.”


Reference:

Sundqvist, E., et al., 2012. Atmospheric methane removal by boreal plants. Geophysical Research Letters, 39, L21806, doi:10.1029/2012GL053592