Comforting Science For Earth Day
Since it was recently Earth Day, a yearly day of celebration and protest by conservationists and assorted greens, it is instructive to take a look at a number of recent studies taken from the scientific literature. The dire predictions made by climate change alarmists are many, far to numerous to all be addressed here, so this article will examine three areas of concern: increased drought, destruction of the world's rainforests, and the die-off of ocean coral reefs. Each of these reported calamities has been linked to increasing anthropogenic greenhouse gas emissions and that supposed bane of nature, anthropogenic global warming (AGW). These threats have been repeated ad nauseum by talking heads and climate change activists, but the truth is that these predicted outcomes are not as threatening as they would have you believe.
First we assess increased frequency and severity of drought. Even President Barrack Obama—who certainly qualifies as a talking head who is ignorant of science—has referred to increasing drought as a consequence of global warming in speeches. Many studies have attributed the severity and duration of recent droughts to global warming. The Fourth Assessment Report (AR4) of the UN Intergovernmental Panel on Climate Change (IPCC) summarized the evidence as follows: “More intense and longer droughts have been observed over wider areas since the 1970s, particularly in the tropics and subtropics. Increased drying linked with higher temperatures and decreased precipitation has contributed to changes in drought.”
Trouble is, the AR4 report depended heavily on historic analyses of the Palmer Drought Severity Index (PDSI), which shows an increase in regional and global drought in the last few decades. Since that appeared to go hand in hand with the increase in global temperatures, totally agreeing with the IPCC author's expectations, this was counted as fact and confirmation of the dangers of AGW. But not so fast.
Recently, there have been a number of recent studies, all of which indicate no statistically significant change in drought world wide. One example is a study in the journal Nature, titled “,” by Justin Sheffield, Eric F. Wood and Michael L. Roderick. In the abstract they state the warmist party line (global warming causes drought), identify a problem (the way drought was measured is inaccurate) and give the findings of their reassessment.
Drought is expected to increase in frequency and severity in the future as a result of climate change, mainly as a consequence of decreases in regional precipitation but also because of increasing evaporation driven by global warming. Previous assessments of historic changes in drought over the late twentieth and early twenty-first centuries indicate that this may already be happening globally. In particular, calculations of the Palmer Drought Severity Index (PDSI) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed, in part, to global warming. The simplicity of the PDSI, which is calculated from a simple water-balance model forced by monthly precipitation and temperature data, makes it an attractive tool in large-scale drought assessments, but may give biased results in the context of climate change. Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation that responds only to changes in temperature and thus responds incorrectly to global warming in recent decades. More realistic calculations, based on the underlying physical principles that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years.
The PDSI was developed originally as an agricultural monitoring tool in the United States in the 1960s. It became popular in climatological circles because it was easy to calculate and had a fairly long history. Trouble is, the PDSI has several shortcomings because of its simplicity, many of which are expounded on in detail in the paper by Sheffield et al.. Even in the US the failings of the old methodology has forced a reassessment of drought over the past century. NOAA has shifted to the PMDI, the Palmer Modified Drought Index. Here is NOAA's latest update on drought in the continental US over the last century.
Drought in the US according to NOAA.
In fact, if you download the raw data and do a linear regression to find the trendline, it is slightly negative—drought is diminishing, at least in the US. Perhaps Obama should consult his government scientists before he repeats climate alarmist drivel. To judge by the drought index there has been no noticeable global warming. Indeed, recent investigations have pointed to droughts as a cause of rising temperatures, not the other way round.
Dying Tropical Forests
Another trouble area is the world's tropical forests, which lock up a significant amount of carbon. Tropical forests store approximately 470 billion tons of carbon in their biomass and soil, and are responsible for about one-third of global terrestrial plant growth. They regulate local meteorology and house a disproportionate amount of global biodiversity. In a letter published in Nature Geoscience, titled “Simulated resilience of tropical rainforests to CO2-induced climate change,” Chris Huntingford et al. subjected simulated tropical forests to the ravages of climate change as predicted by 23 climate models and found that the outcomes were not as dire as previously predicted. The map below shows the parts of the world being addressed.
Map of the world's tropical forests.
Shown are tropical land regions and model gridboxes predicted to have more than 85% cover of forest for pre-industrial climate (continuous and dashed black outlines). The green dots are from satellite observations of where there is mainly evergreen tropical forest, based on the GLC2000 land cover map. The gridboxes used have continuous black outlines. The 15 gridboxes outlined with dashed lines were not included in the analysis as these areas contain little (<10%) observed forest cover, despite the model predicting higher coverage (see larger image).
This is another of those computer generated reports that includes dozens of plots with so many curves on each that much meaning is lost in cluttered rainbow colored displays. You can peruse the graphs below, which show change in biomass for the three main areas of the study: the Americas (a), Africa (b) and Asia (c).
Predicted biomass change..
Note that the preindustrial level is taken from estimates of forest extent in 1860. The result: “Forest biomass carbon stocks in Asia and Africa are projected to be greater in year 2100 than at the present day, in all simulations.” The Americas are the only area that shows a decrease and then only under one simulation. Here is the authors summary.
We find the possibility of climate-induced (that is, not direct deforestation) damage to tropical rainforests in the period to year 2100, even under the SRES A2 business-as-usual emissions scenario, might be lower than some earlier studies suggest. For instance, our MOSES–TRIFFID model configuration predicts undisturbed tropical forests as always sequestering carbon to mid twenty-first century, and possibly beyond for most climate models.
It is a remarkable result—more biomass means more plants, which in turn means more forest. It would appear that, in the absence of other human activity like logging and land clearing, the tropical rainforests are going to be just fine. Do not misunderstand, humanity is having a negative impact on the world's tropical forests, just not through CO2 emissions or global warming.
Ravaged Coral Reefs
Coral reefs have become a staple for global warming reporting; it seems that there are always some reefs, some where, that are becoming bleached out or dying. America's National Public Radio recently did yet another series of reports on the reefs north of Australia in the run-up to Earth Day. One should never expect the scientists studying corals to say that the reefs are not in trouble—if there is no problem there is little urgency behind their research (or funding for that research). Still there are many interesting reports running around in the scientific literature that indicate coral is tougher than portrayed in the media.
On case in point can be found in a news article in Nature. In an article titled “Why some corals can take the heat,” it is reported that researchers have uncovered a pattern of gene activity that enables some corals to survive in higher temperatures. The finding suggests a way to predict how different corals will behave if water temperatures increase.
A bleached coral reef.
Reportedly, some of the Acropora hyacinthus corals in the back reef of Ofu Island, American Samoa, are able to thrive in pools that experience daily heat fluctuations of up to 6 °C. The actual results were recently published in the Proceedings of National Academy of Sciences (PNAS) in an article titled “Genomic basis for coral resilience to climate change,” by Daniel J. Barshis et al.. Here is the abstract:
Recent advances in DNA-sequencing technologies now allow for in-depth characterization of the genomic stress responses of many organisms beyond model taxa. They are especially appropriate for organisms such as reef-building corals, for which dramatic declines in abundance are expected to worsen as anthropogenic climate change intensifies. Different corals differ substantially in physiological resilience to environmental stress, but the molecular mechanisms behind enhanced coral resilience remain unclear. Here, we compare transcriptome-wide gene expression (via RNA-Seq using Illumina sequencing) among conspecific thermally sensitive and thermally resilient corals to identify the molecular pathways contributing to coral resilience. Under simulated bleaching stress, sensitive and resilient corals change expression of hundreds of genes, but the resilient corals had higher expression under control conditions across 60 of these genes. These “frontloaded” transcripts were less up-regulated in resilient corals during heat stress and included thermal tolerance genes such as heat shock proteins and antioxidant enzymes, as well as a broad array of genes involved in apoptosis regulation, tumor suppression, innate immune response, and cell adhesion. We propose that constitutive frontloading enables an individual to maintain physiological resilience during frequently encountered environmental stress, an idea that has strong parallels in model systems such as yeast. Our study provides broad insight into the fundamental cellular processes responsible for enhanced stress tolerances that may enable some organisms to better persist into the future in an era of global climate change.
Ignoring the end of the last sentence, which is the obligatory nod to climate science orthodoxy, the findings here are both interesting and not unexpected. The paper says that some corals posses greater resistance to temperature fluctuations than others, probably because they have experienced such change in the past. This certainly makes sense, since it is well known that there have been other periods of higher global temperature than today. It was hotter for a prolonged period during the Holocene Climate Optimum (8,000-5,000 years ago), yet somehow the reefs survived. Paleoclimate records indicate that the previous interglacial period, the Eemian, was 4-8°C hotter than today so ancient corals withstood the heat and persisted in the world's oceans. Why are people surprised to find that some, not all, corals can handle higher temperatures?
Again according to Nature (see “Contemplating a coral comeback”) the Great Barrier Reef has lost about half its coral over the past 27 years, according to data from more than 2,000 surveys of 214 reefs. But the proximate cause of the decline is not global warming. As reported in a paper in PNAS by Glenn De'ath et al. this is how the damage breaks down:
Based on the world’s most extensive time series data on reef condition (2,258 surveys of 214 reefs over 1985–2012), we show a major decline in coral cover from 28.0% to 13.8% (0.53% y−1), a loss of 50.7% of initial coral cover. Tropical cyclones, coral predation by crown-of-thorns starfish (COTS), and coral bleaching accounted for 48%, 42%, and 10% of the respective estimated losses, amounting to 3.38% y−1 mortality rate. Importantly, the relatively pristine northern region showed no overall decline. The estimated rate of increase in coral cover in the absence of cyclones, COTS, and bleaching was 2.85% y−1, demonstrating substantial capacity for recovery of reefs. In the absence of COTS, coral cover would increase at 0.89% y−1, despite ongoing losses due to cyclones and bleaching. Thus, reducing COTS populations, by improving water quality and developing alternative control measures, could prevent further coral decline and improve the outlook for the Great Barrier Reef.
Let me repeat that, bleaching attributable to global warming accounts for only 10% of the damage. It would seem that if Australia wishes to save its reefs it should seek a way to prevent starfish outbreaks. There is some indication that reducing nutrient run-off to the area, would allow the coral to recover at a rate of up to 1% per year. Of course curbing agricultural runoff is not nearly as sexy as fighting global warming, and agriculture has political clout. Much safer to seek government funding to assess the ravages of climate change.
A recovered coral reef.
Strangely, bleaching can be caused by a significant drop in temperature as readily as an increase. In January 2010, cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral death. Water temperatures dropped -6.7°C (12.1°F) lower than temperatures typically observed at that time of year. The damaged reefs have mostly recovered. For more information on reef recovery see the Reef Resilience website or read “Bleached Coral Reefs Bounce Back,” previously posted on this blog. Corals have been on Earth 100 times longer than mankind, that should tell us something.
So take heart, things are not as dire as some would have us believe: Drought is not more frequent or more severe; Tropical forests are not dying, at least not because you drive an SUV or have a barbeque grill; and coral reefs are tougher than the “experts” thought. We surely must strive to be good stewards of the planet we live on, because we do possess the ability to make a god awful mess of things. But this does not mean we need to dismantle human civilization and return to our “roots” as bands of hunter-gatherers, foraging for food at the mercy of capricious nature. If we take care of Earth, it will take care of us—most of the time. There will still be disasters, to be sure, but that's the way life is—uncertain. What we do not need, in addition to the uncertainty provided by nature, are a bunch of misanthropic tree-huggers who are ignorant of nature and befuddled by modern day living, telling us what we must do. They can bugger off. Everyone else, Happy Earth Day!
Be safe, enjoy the interglacial and stay skeptical.