The Climate Change Context

Climate change, scientific consensus increasingly suggests, represents one of the single most important challenges global society will face over coming decades and centuries. 

Understanding regarding the impacts of climate change has evolved substantially in recent years. Until the Fourth Assessment Report is published by the IPCC later this year, the most up to date summary of changes in climate and their likely impact is contained in the Stern Review on the Economics of Climate Change (Stern, 2006).  This review emphasizes the manner in which the costs associated of climate change increase as the average temperature increases.  As the figure below, copied from the review, highlights even a 1^o C change will be sufficient to cause major impacts while changes of 2-3^o C or more will cause massive disruption.  According to the review:  “The current stock of greenhouse gasses in the atmosphere is equivalent to around 430 parts per million (ppm) C0₂, compared with 280ppm before the Industrial Revolution.  These concentrations have already caused the world to warm by more than half a degree Celsius and will lead to at least a further half degree warming over the next few decades, because of inertia in the climate system (Stern, 2006, p. iii).” They further point out that given the accelerating rate of emissions, the concentration could reach 550ppm “as early as 2035” virtually[1] committing the world to an average temperature rise exceeding 2^o C.  The average level of warming is, however, simply an indicator of the impacts, not the full story.

As the review states: “People will feel the impact of climate change most strongly through changes in the distribution of water around the world and its seasonal and annual variability” (Stern, 2006, p. 62). At an average global temperature increase of 2-3^o C, the water related impacts of climate change highlighted in a figure prepared for the executive summary of the review (Stern, 2006, p. v) include:

In addition to the specific impacts included in the diagram, the review notes that a 2-3^o C rise would lead to “many severe impacts, often mediated by water, including more frequent droughts and floods.” (Stern, 2006, p. 56)  This level of warming could also “induce sudden shifts in regional weather patters like the monsoons or the El Nino.  Such changes would have severe consequences for water availability and flooding in tropical regions and threaten the livelihoods of billions.” (Stern, 2006, p. 56 - document attached).

The water related impacts of climate change are likely to vary greatly between regions.  According to the Stern review, recent modeling results suggest that with a 2^o C rise in average temperature, South Asia, parts of Northern Europe and Russia will experience significant increases in runoff while other regions – notably the Mediterranean, Southern Africa and South America – will experience large decreases.  Average runoff is, however, only a small part of the water story.  If, as most projections suggest, the variability and intensity of weather events increase, even increases in average runoff may not increase the supply available to meet human and ecosystem requirements.  As the Stern review notes: “an increase in annual river flows is not necessarily beneficial, particularly in highly seasonal climates, because: (1) there may not be sufficient storage to hold the extra water for use during the dry season, and (2) rivers may flood more frequently.” (Stern, 2006, p. 62) In South Asia, for example, the Stern review specifically notes that “much of the extra water will come during the wet season and will only be useful for alleviating shortages in the dry season if storage could be created (at a cost).  The additional water could also give rise to more serious flooding during the wet season.” (Stern, 2006, p. 63).

Given likely increases in floods, droughts and other extreme climatic events, disaster risk reduction will need to form a core part of any strategy for adapting to climate change.  Regions, such as the Gangetic Basin, where flooding is already an issue will need to develop effective risk reduction strategies that are capable of addressing anticipated increases in variability.  This is also the case for many drought prone regions.  Among the regions most vulnerable to extreme events will be low-lying coastal areas.   In the intervening few months since the Stern Review was published, additional information on the impacts of climate change has been published that highlights risks for coastal areas.  According to an article in the International Herald Tribune[2], melting of glacial and sea ice in Greenland appears to have abruptly accelerated.  Greenland alone could be losing more than 333 cubic kilometers of ice per year with ice margins retreating, in some cases, by two kilometers per year. Richard Alley, a geosciences professor from Pennsylvania State University quoted in the article suggested that, given the acceleration in melting, a sea-level rise of a foot or two in the coming decades is entirely possible.  Substantial rises in sea-level would greatly compound the impact of extreme climatic events on coastal areas.

The impacts of any increase in climatic variability are also likely to be compounded by preexisting patterns of environmental degradation. In India, for example, groundwater overdraft caused by intensive groundwater development for agriculture has been emerging as a major point of concern for policy makers since the early 1990s (World Bank and Ministry of Water Resources - Government of India 1998).  Groundwater has served as the primary water resource input stabilizing Indian agriculture and enabling increases in production using green revolution technologies.  Increases in average precipitation might increase groundwater recharge but this is not necessarily the case if the additional precipitation occurs in intense events.  Recharge rates are limited by the infiltration capacity of soils.  Instead of adding to recharge, intense storms, particularly if they occur during the wet season when the soil is already saturated, generate additional runoff but, due to fixed infiltration rates, little additional recharge.  As a result, additional rainfall during the wet season may not contribute to additional water availability during the dry season.  Where aquifers are already experiencing overdraft, dry-season scarcity could increase dramatically with increases in variability.

The impact of this type of dynamic could be further compounded by changes in snow and glacier melt patterns in melt-water fed river basins.  Most projections of global warning have identified changes in precipitation and melt patterns as a likely impact of changes in average global temperatures.  More precipitation is likely to fall as rain and snow melt is likely to occur earlier in the season.  This may already be occurring.  Glaciers in the Himalayan region have been retreating rapidly for decades and, as the Stern review also notes, with higher levels of warming they could disappear entirely.  At present, according to the Stern review, glacial melt provides 70% of the summer flow in the Ganges.  Surface water scarcity during the dry season, a problem in parts of the Gangetic basin even now, is likely to increase.  At the same time with increases in overall precipitation – and more of that occurring as rain – flooding during the wet season is also likely to increase.

Dynamics such as the above will interact with existing environmental conditions and patterns of development in the basin.  Dry season scarcity will increase incentives to pump groundwater and, unless recharge increases correspondingly, this will contribute to the already present rates of water level decline in key aquifers.  This could further decrease dry-season base flows in streams (much of which comes from groundwater).  In addition, recent publications indicate that, in order to maintain the same level of irrigation service (i.e. the same volume pumped) every meter decline in groundwater levels increases the GHG emissions in some Indian states by 4-6% due to the increased energy required for pumping (Mall, Gupta et al. 2006).  In sum, the impacts of increases in climatic variability are likely to be compounded by existing water problems such as groundwater overdraft and that these could, in turn, further contribute to emissions concerns. 

Impacts summarized by the Stern review are, in many ways, nothing new.  The IPCC Third Assessment report (IPCC 2001) identified many of the issues raised by the Stern Report.  Given increases in scientific knowledge since publication of the Third Assessment Report, the soon to be published Fourth Assessment Report is likely to further emphasize both acceleration of climate change processes and their impacts.  Many of the processes will be gradual but their impacts are likely to be felt most intensely in conjunction with extreme events. The importance of small changes in sea level (an incremental change) for storm surges (a pulsed change) is widely recognized.  A similar conjunction of impacts may occur when, for example, intense droughts occur in regions where precipitation or dry season flows have been declining incrementally over a long period or when intense storms occur in regions that are already saturated due to long-term increases in precipitation.  Conceptually, as a result, the challenge is to develop strategies for adaptation that are capable of responding to both the incremental changes that can be anticipated and, probably more importantly, to changes that are either impossible to predict or where the changes will occur in a pulsed manner with the specific timing and magnitude subject to high levels of uncertainty. 

Understanding of pulsed change processes and the practical mechanisms for addressing them, including specific initiatives to reduce disaster risk, will be essential in order to respond to climate change.

References:

IPCC (2001). Climate  Change 2001: Synthesis Report Summary for Policymakers. Wembly, Intergovernmental Panel on Climate Change: 34.

Mall, R. K., A. Gupta, et al. (2006). "Water resources and climate change: An Indian perspective." CURRENT SCIENCE 90(12).

[1] Depending on the model used, this level has between a 77% and 99% chance of causing an average rise of more than 2^o C.

[2] John Collins Rudolf, Glaciers’ retreat in Greenland keeps mapmakers busy, International Herald Tribune, January 16, 2007.  Web edition: www.iht.com/articles/2007/01/16/news/warm.php