Tag: global warming

A 1,000-Year History of Eastern Australia Megadroughts: How Do They Compare with the Recent Occurrence of the “Big Dry”?

Drought is a common feature of climate; but every so often when a longer-lasting or somewhat severe drought occurs, it is not long before someone, somewhere, makes the claim that that drought was either caused or made worse by CO2-induced global warming. A simple test of this thesis can be conducted by examining the historic record of drought for the location in question. If it can be shown that similar (or greater) frequencies or magnitudes of drought have occurred in the past, prior to the modern increase in CO2, then it cannot be definitively concluded that the current drought is the product of anything other than natural climate variability.

Unfortunately, long-term historical drought records covering more than a few decades of time are lacking for most locations across the planet. As a result, scientists have sought to augment these short-term instrumental drought histories with much longer proxy records, records that will sometimes extend back in time several centuries to millennia. Such is the case in the recent study of Vance et al. (2015), who derived a 1,003-year proxy of historical drought in eastern Australia.

Two Millennia of Snowfall Accumulation in Antarctica

Providing the rationale for their work, Roberts et al. (2015) write that “the short and sparse instrumental record in the high latitudes of the Southern Hemisphere means investigating long-term precipitation variability in this region is difficult without access to appropriate proxy records.” It was therefore the objective of this team of nine researchers to extend the duration of the Law Dome, East Antarctica, snowfall accumulation record back in time an additional 750 years so that it would cover over two millennia.

The resultant 2035 year-long proxy (22 BC to 2012 AD) is presented in the figure below. As reported by the authors, the average long-term snow accumulation rate was calculated as 0.686 m yr-1 (27 inches) ice equivalent, which rate they say “is in agreement with previous estimates, and further supports the notion that there is no long-term trend in snow accumulation rates, or that any trend is constant and linear over the [2035-year] period of measurement.”

If this number seems low for such an icy continent, the fact is that most high-latitude locations in both hemispheres would qualify as deserts based upon annual precipitation. In many places, it is literally “too cold to snow” as the frigid air can hold only tiny amounts of moisture.

There were several decadal-scale oscillations in the record, described by the authors as “common,” with “74 events (33 positive and 41 negative) of at least a 10-year duration in the record.”  The three longest periods of above average integrated snowfall occurred over the intervals 380-442, 727-783, and 1970-2009, while the three longest periods of below average integrated snowfall occurred during 663-704, 933-975, and 1429-1468.

On the Bright Side: Tropical Cyclones in the Bay of Bengal During Warmer and Colder Phases of ENSO and the PDO

While the hypothesis that tropical cyclones will become both more frequent and more intense as planetary temperatures rise has long been debated, real-world evidence has consistently refuted it (see, for example, the many reviews of this subject posted under the heading of Hurricanes at the CO2 Science website). The latest example is the work of Girishkumar et al. (2015), who examined over five decades of tropical cyclone (TC) data from the Bay of Bengal (BoB) in the Indian Ocean. Specifically, the authors “investigated how the relationship between ENSO and TCs activity in the BoB during October–December varies on decadal time scale with respect to PDO.”

China Recycles: Another Attempt at Cap and Trade

China’s announcement of the implementation of a cap and trade system is not the first we’ve heard of their efforts to combat their rising carbon emissions. In November, China and the United States hyped an agreement in which China “intends” to curb emissions “around” 2030. Reproduced below is an article on that “agreement,” which will certainly be greatly referenced over the course of Xi Jinping’s visit.

For today’s announcement, as with all international pronouncements on climate change, we must wait until we see the fine print. The road to global warming has traditionally been paved with good intentions.

On The Bright Side: Declining Deaths Due to Hot and Cold Temperatures in Hong Kong

Global warming theory predicts increased mortality due to global warming, but observations frequently suggest the opposite. The newest case-in-point comes from a study by Chau and Woo (2015).

Setting the stage for their enlightening new study, the pair of researchers note there is a growing concern about the potential impacts of global warming on human mortality, where some researchers estimate future increases in heat-related deaths will outnumber future decreases in cold-related deaths. In a test of this hypothesis, the two Chinese scientists examined summer (June-August) versus winter (December-February) excess mortality trends among the older population (65 years and older) of Hong Kong citizens over the 35-year period 1976-2010. This was accomplished through the performance of statistical analyses that searched for relationships between various measures of extreme meteorological data and recorded deaths due to cardiovascular and respiratory-related causes. And what did those analyses reveal?

With respect to the weather, Chau and Woo report there was an average rise in mean temperature of “0.15°C per decade in 1947–2013 and an increase of 0.20°C per decade in 1984–2013.” They also note that over the 35-year period of their analysis “winter became less stressful” with fewer extreme cold spells. Summers, on the other hand, became “more stressful as the number of Hot Nights in summer increased by 0.3 days per year and the number of summer days with very high humidity (daily relative humidity over 93%) increased by 0.1 days per year.” Given such observations it would be expected—under global warming theory—that cold-related deaths should have declined and heat-related deaths should have increased across the length of the record. But did they?

The Resilience of an American Pika Metapopulation to Global Warming

The American pika (Ochotona princeps) is an insanely cute critter often found in above-timberline rock fields in the western U.S.  

A Pika

Because they often live near mountain peaks, there’s been concern that global warming could push them over the top, to extinction. Writing in the Journal of Mammalogy, Smith and Nagy (2015) state that American pikas (Ochotona princeps) “have been characterized as an indicator species for the effects of global warming on animal populations,” citing the works of Smith et al. (2004), Beever and Wilkening (2011) and Ray et al. (2012). Indeed, as they continue, “a consideration of the effects of climate, primarily recent warming trends due to climate change, has dominated much of the recent literature on American pikas and their persistence.” Hoping to provide some additional insight on the subject, the two Arizona State University researchers set out to investigate the resilience of a pika metapopulation residing near Bodie, California, USA, that was exposed to several decades of natural warming.

Tree-ring Temperature Reconstructions May have Masked Prior Warmth

Global Science Report is a 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.”

Proxy temperature records serve a significant purpose in the global warming debate – they provide a reality check against the claim that current temperatures are unprecedentedly warm in the context of the past one to two thousand years. If it can be shown that past temperatures were just as warm as, or warmer than, they are presently, the hypothesis of a large CO2-induced global warming is weakened. It would thus raise the possibility that current temperatures are influenced to a much greater degree by natural climate oscillations than they are by rising atmospheric CO2.

Tree ring data account for one of the most commonly utilized sources of proxy temperatures. Yet, as with any substitute, proxy temperatures derived from tree ring data do not perfectly match with standard thermometer-based measurements; and, therefore, the calculations and methods are not without challenge or controversy. For example, many historic proxies are based upon a dwindling number of trees the further the proxy extends back in time. Additionally, some proxies mix data from different trees and pool their data prior to mass spectrometer measurement, which limits the ability to discern long-term climate signals among individual trees. Though it has the potential to significantly influence a proxy record, this latter phenomenon has received little attention in the literature – until now.

In an intriguing new study, Esper et al. (2015) recognize this deficiency by noting “climate reconstructions derived from detrended tree-ring δ13C data, in which δ13C level differences and age-trends have been analyzed and, if detected, removed, are largely missing from the literature.” Thus, they set out to remedy this situation by developing “a millennial-scale reconstruction based on decadally resolved, detrended, δ13C measurements, with the climate signal attributed to the comparison of annually resolved δ13C measurements with instrumental data.” Then, they compared their new proxy with proxies derived from a more common, but presumably inferior, method based on maximum latewood density (MXD) data. The location of study was at a sampling site near lake Gerber (42.63°N, 1.1°E), Spanish Pyrenees, at the upper treeline (2400 m).