In the news this week...

THAWING PERMAFROST DECREASES RUNOFF TO THE RIVER YANGTZE

Researches at the Chinese Academy of Sciences (CAS) have observed a 15% decrease in runoff entering the river Yangtze over the last four decades despite increases in glacial melt and precipitation (Qui, 2012). This contrasts from other rivers surveyed in western China such as Tarim river which showed a 13% increase in input into the river coinciding with a 26% increase in glacial melt since 1961.

The decrease in the input to the Yangtze river was attributed to changes in permafrost on the Tibetan Plateau, the source of the Yangtze headwaters. The causes for this feedback are still uncertain however, Wang et al., (2012) suggest either the increase in the active ground layer  at some sites has reduced surface runoff as more water is infiltrating into the upper surface layer or more water may be percolating through the the surface as groundwater. Dependent on air temperature and vegetation cover, degradation of wetland habitats on the plateau is also contributing to reduced runoff causing a different discharge pattern to other regions of China and general patterns worldwide (Qui, 2012). 

This article highlights the importance that permafrost can have in altering the response of river discharge to glacial melt. Ge (2012 cited in Qui, 2012) states that permafrost contributes up to a quarter of the earth's surface and could be 'just as important [as glaciers] in terms of water resources, especially in places such as the Tibetan Plateau'. The findings from this article underline the complexity of predicting changes to water resources in the Himalayas and the importance of further basin-level research that accounts for all of the processes affecting river discharge.

STUDY COMPARING RECENT WARMING AGAINST THE PALEOCLIMATIC RECORD

Using ice cores from the Arctice and Antarctica and deep ocean sediment cores, Hansen and Sato (2011) compared the current climate against two previous interglacials: Eemian and Holsteinian period (also known as Marine Isotope Stages 5e and II respectively). Despite some discrepencies between the ocean and ice cores, overall the proxy data suggests current global temperature is only 1°C lower than during the Eemian period. Therefore, Hanson and Sato (2011:17) argue that target set for maximum 2°C temperature rise is inadequate as it would exceed temperatures during the Eemian interglacial where sea-levels were approximately 4-6 metres higher than present, and would raise global temperatures closer to those observed for the Pliocene where sea level had been around 25 metres higher than current levels. Recognising that ice disintegration is a non-linear process Hanson and Sato (2011) suggest that for every 1°C rise in temperature, sea-level will rise by 20 metres suggesting an increase in sea level by several metres by 2100. Accepting some slow feedbacks to current global temperatures means further rises are highly likely, Hanson and Sato (2011) suggest carbon dioxide levels need to be reduced to 350ppmv (compared to present level of 390ppmv) to stabilise increases in global temperature to 1°C.

Using paleoclimatic data in research is essential in order to put current environmental changes into perspective. Findings from this paper suggest the 2°C limit set by government organisations may be inadequate, and Hanson and Sato (2011) claim this limit was set on what is politically realistic rather than on scientific research. A highly controversial statement this paper demonstrates that despite warmer periods occurring in the past, the current rate of temperature increase is unprecedented in the historical record.

Global temperature relative to the Holocene based on ocean proxy record where levels have been amplified by 1.5 to provide an estimate for surface values (Source Hanson and Sato, 2011: 20)

Reference:
Hanson, J. E. and M. Sato (2011) Paleoclimate Data for Human-made Climate Change, NASA Goddard Institute for Space Studies: New York, 1-32.

Qui, J. (2012) 'Thawing permafrost reduces runoff', Nature, 9749.