March 23, 2011

Global Greening Continues: Did We Cause It?

You know the story. Humans are burning fossil fuels and because of their actions, the world is now warming at an unprecedented pace. This warming is stressing ecosystems throughout the world with devastating consequences to vegetation from one end of the earth to the other. If we do not act fast, we will destroy the planet and have a tough time facing our grandchildren. We can all hear it now—why didn’t you do something when there was still time to save the Earth?

Two articles have appeared recently in the scientific literature with results that may make us reconsider this entire affair. The first appears in the Journal of Geographical Sciences dealing with worldwide trends in the vigor of vegetation since the early 1980s—the results may surprise you, but they did not surprise us given all that has been written on this subject and certainly covered at World Climate Report.

Three Chinese scientists (all with the last name of Liu) used satellite data to detect changes occurring in vegetation throughout the world. Rather than use the popular satellite-based Normalized Difference Vegetation Index (NDVI), Liu et al. (a.k.a., Liu3) decided to use the Leaf Area Index (LAI). The scientists explain “LAI, defined as half the total leaf area per unit ground, is directly linked to vegetation activities and comparable among different ecosystems. It has removed the effects of spectral response, illumination and orbit drift during data acquisition. It should be better, at least theoretically, than NDVI as the indicator of vegetation status.” We will certainly trust their judgment.

As seen in their figure below (Figure1), the red colors absolutely dominate indicating an increase in vegetation status! Liu et al. declare:

“Results show that, over the past 26 years, LAI has generally increased at a rate of 0.0013 per year around the globe. The strongest increasing trend is around 0.0032 per year in the middle and northern high latitudes (north of 30°N). LAI has prominently increased in Europe, Siberia, Indian Peninsula, America and south Canada, South region of Sahara, southwest corner of Australia and Kgalagadi Basin; while noticeably decreased in Southeast Asia, southeastern China, central Africa, central and southern South America and arctic areas in North America.”

Quick geography question: where is the “Kgalagadi Basin”? Correct—in the Kalahari Desert of southern Africa.


Figure 1. Spatial distribution of linear trends in estimated LAI from July 1981–December 2006 (from Liu et al., 2010)

In commenting on the upward trend in LAI in the mid-to-high latitudes of the Northern Hemispheric, the trio states

“The growth of the vegetation in these middle and high latitude areas is mainly limited by temperature. Many studies correlating NDVI with land surface temperature indicate warming might be the most important factor accounting for the LAI increase in this area. Warming, causes longer active growing season length and higher growth magnitude, therefore leads to increase in LAI in this area.”

We accept their findings—we now believe that warming has been beneficial for vegetation throughout much of the Northern Hemisphere. As we look at the map above, we see red throughout many low latitude areas as well. The gloom and doomers of the climate change issue are not going to be happy with such positive results. Although not discussed in the Liu et al. paper, we cannot help but wonder what role elevated carbon dioxide (CO2) concentrations may have played in stimulating plant growth in so many areas of the world? Feel free to examine all of our essays reporting on the biological benefits of elevated CO2, let alone the benefits of warming.

Few people would argue that the planet has warmed to some extent over the past three decades, and many people feel that humans caused at least some part of this warming through their consumption of fossil fuels. Well, hold the fort because our second featured article does not arrive at that conclusion whatsoever. The article was written by two scientists from Taiwan and was published recently in Atmospheric Science Letters. Lo and Hsu begin stating:

“The global mean temperature has been rising more abruptly over the past 30 years, compared with that in the previous 50–100 years. This recent warming has occurred in most areas on Earth, becoming a truly global phenomenon. The sudden acceleration of warming, which is particularly evident in the winter Northern Hemisphere (NH), can be linked with the observation of widespread abrupt changes in the late 1980s. The nature of the late 1980s’ warming and its relationship with the dominant teleconnection patterns such as the Arctic Oscillation (AO) and the Pacific Decadal Oscillation (PDO) are explored in this study.”

We knew we would like this—nothing better than scientists explaining warming with teleconnections related things that operate largely without any association to the buildup of greenhouse gases. The authors conducted sophisticated research with climate models and greenhouse gas scenarios developed by the United Nations’ IPCC group. They found that warming in the extra-tropical Northern Hemisphere was highly related to the two teleconnections, and it led them to conclude (hold your breath) that their results “do not support the scenario that the emerging influence of the AO-like pattern in the late 1980s can be attributed to the anthropogenic greenhouse effect.” Indeed, they conclude that what we are seeing “can be attributed to natural variability.”

OK. The earth warmed over the past 30 years. We agree (although that has largely slowed down or even stopped in the past 10 years). Atmospheric CO2 has increased. We agree. The rise in CO2 caused the warming—not according to Lo and Hsu. The warming caused vegetation in the Northern Hemisphere to thrive—Liu et al. think so.

You get the message—warming and elevated CO2 are not combining to destroy the planet’s vegetation. Quite to the contrary, they may be a blessing!

References

Lo, T.-T. and H.-H. Hsu. 2010. Change in the dominant decadal patterns and the late 1980s abrupt warming in the extratropical Northern Hemisphere. Atmospheric Science Letters, 11, 210–215.

Liu, S., R. Liu, and Y. Liu. 2010. Spatial and temporal variation of global LAI during 1981–2006. Journal of Geographical Sciences, 20, 323-332.




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