The Azimuth Project
Possible effects of global warming (Rev #7)


This page will list the major possible effects of global warming and provide references to current research on this subject. It is meant to include effects that are certainly happening or most likely happening as well as merely possible effects. So, the inclusion of an effect on this list is not in itself a comment on whether the effect is certain, likely, or merely possible.

Extreme weather events

The role of global warming in causing floods, droughts and other extreme weather events is much argued. It is particularly difficult to attribute individual events to global warming, but in February 2011 two papers appeared on this topic.

  • Pardeep Pall, Tolu Aina, Dáithí Stone, Peter Stott, Toru Nozawa, Arno Hilberts, Dag Lohmann, and Myles Allen, Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000, Nature 470 (17 February 2011), 382–385.

Abstract: Interest in attributing the risk of damaging weather-related events to anthropogenic climate change is increasing. Yet climate models used to study the attribution problem typically do not resolve the weather systems associated with damaging events such as the UK floods of October and November 2000. Occurring during the wettest autumn in England and Wales since records began in 1766, these floods damaged nearly 10,000 properties across that region, disrupted services severely, and caused insured losses estimated at £1.3 billion. [] Here we present a multi-step, physically based ‘probabilistic event attribution’ framework showing that it is very likely that global anthropogenic greenhouse gas emissions substantially increased the risk of flood occurrence in England and Wales in autumn 2000.

This paper is not freely available online yet, but the supplementary online information is free and interesting. It begins:

A popular simple thermodynamic argument assumes precipitation extremes are constrained to change with the water vapour capacity of the atmosphere that can be determined, under conditions of constant relative humidity, using change in mean surface temperature alone according to the Clausius-Clapeyron relation38. This argument is typically invoked in the aftermath of floods as an explanation for possible increases in such severe wet events under an anthropogenically warming climate.

While this is an oversimplified treatment not fully accounting for the complex hydrometeorology typically associated with UK flooding, it may nevertheless provide a physically plausible first guess of increases in mid-latitude precipitation extremes under warming. Indeed, a recently updated analysis of observed atmospheric column water vapour for past decades finds increasing trends over the UK and western Europe, and a significant autumnal increase more generally over Europe and the Northern Hemisphere; and this appears in agreement with a similar analysis finding increases in observed atmospheric humidity under warming for these regions that are within expected moistening rates for near-constant relative humidity.This latter analysis in particular appears broadly consistent with observations of Clausius-Clapeyron scale increases in surface specific humidity (the principle source for the free-troposphere) under warming over past decades, again with near-constant relative humidity – including for an European region incorporating the UK. Since these surface specific humidity increases have been attributed to mainly anthropogenic drivers, this lends support to a thermodynamic mechanism for increasing UK precipitation, and hence flooding, under anthropogenic warming.

Here we use this thermodynamic argument to deduce the reduction in observed England and Wales total daily precipitation extremes for an autumn 2000 climate, had estimated twentieth-century surface warming attributable to anthropogenic greenhouse gas emissions not occurred. Then regarding this reduction in precipitation extremes as a direct measure of reduction in flooding, we calculate the fraction of attributable risk (FAR) of these extremes, and compare it to the FAR of autumn 2000 flooding explicitly modelled in terms of severe daily river runoff using our more rigorous multi-step probabilistic event attribution (PEA) framework of the main text.

This related abstract is also available:

The second paper appearing in February 2011 is:

  • Seung-Ki Min, Xuebin Zhang, Francis W. Zwiers and Gabriele C. Hegerl, Human contribution to more-intense precipitation extremes, Nature 470 (17 February 2011), 378-381.

Abstract: Here we show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas. […] Changes in extreme precipitation projected by models, and thus the impacts of future changes in extreme precipitation, may be underestimated because models seem to underestimate the observed increase in heavy precipitation with warming.

Again this paper is not yet available for free online, but there’s a discussion of it here:

Expansion of the tropical belt

Tropical zone expanding due to climate change: study (2009)

Researchers at James Cook University concluded the tropics had widened by up to 500 kilometres (310 miles) in the past 25 years after examining 70 peer-reviewed scientific articles. (…) Professor Steve Turton said that meant the subtropical arid zone which borders the tropics was being pushed into temperate areas, with potentially devastating consequences. “Such areas include heavily-populated regions of southern Australia, southern Africa, the southern Europe-Mediterranean-Middle East region, the south-western United States, northern Mexico, and southern South America,” he said. “All of (them) are predicted to experience severe drying. ”If the dry subtropics expand into these regions, the consequences could be devastating for water resources, natural ecosystems and agriculture, with potentially cascading environmental, social and health implications.“


  • A. Dai, [Drought under global warming: a review], Wiley Interdisciplinary Reviews: Climate Change 2 (1) (2011), 45–65
Drought projection for 2060s. Click for bigger image.

Vegetation die-off

Abstract: Future drought is projected to occur under warmer temperature conditions as climate change progresses, referred to here as global-change-type drought, yet quantitative assessments of the triggers and potential extent of drought-induced vegetation die-off remain pivotal uncertainties in assessing climate-change impacts. Of particular concern is regional-scale mortality of overstory trees, which rapidly alters ecosystem type, associated ecosystem properties, and land surface conditions for decades. Here, we quantify regional-scale vegetation die-off across southwestern North American woodlands in 2002-2003 in response to drought and associated bark beetle infestations. (…)


Collectively, these observations suggest that the mortality response to the recent drought was greater in magnitude and extent than the mortality response to the 1950s drought. The warmer temperatures associated with the recent drought would have increased the energy load and water stress demands on the trees and may account for the apparently greater resulting mortality.


The cessation of drought conditions may be insufficient for reestablishment of P. edulis and associated plant species, as documented for landscape response of Pinus ponderosa after the 1950s drought (5). Such rapid shifts in vegetation may represent abrupt, rapid, and persistent shifts in not only ecotones, but also in dominant vegetation cover and associated ecosystem process (5, 7-8).

Part of fig. 1 from Breshears et al. from a blog post at

Breshears et al., part of Fig. 1

No More Glaciers in Glacier National Park by 2020?

This is the title of a 2009 National Geographic News story on a U.S. Geological Survey study. Glaciologist Mauri Pelto comments a blog post:

I wish I could say this is sound science, but it is not. All of the glaciers in Glacier National Park have retreated significantly in the last 40 years, and a number have disappeared. This is a compelling story of glacier loss. However, about a third of the remaining glaciers, 10 of 30, have lost less than a quarter of their area since 1966 when the USGS first mapped these glaciers. At this rate they will last well past 2020 or 2030. The focus has been on the rapidly shrinking glacier[s] by this team of non-glacier scientists and they are correct that the Sperry and Grinnell are rapdily declining and will not last for long. However, glaciers such as Jackson and Harrison have lost less than 15% of their area in the last 40 years and will survive well past 2020.

Pelto’s blog, From a Glaciers Perspective has many images of shrinking glaciers and is a top source for news from Greenland to Tasmania. More images on his department pages, where he explains:

Glaciers respond to climate in an attempt to achieve equilibrium. A glacier advances due to a climate cooling/snowfall increase that causes positive mass balance. A climate warming/snowfall decrease leads to negative mass balances and glacier retreat. To reestablish equilibrium a retreating glacier must lose enough of its highest ablating sections, usually at the lowest elevations, so that accumulating snows in the near the head of the glacier once again are equivalent to overall ablation, and an equilibrium balance is approached. If a glacier cannot retreat to a point where equilibrium is established, it is in disequilibrium with the climate system. A glacier that is in disequilibrium with present climate will melt away with a continuation of this climate.

Abstract: (…) In the North Cascades 9 of the 12 examined glaciers exhibit characteristics of substantial accumulation zone thinning; marginal recession or emergent bedrock areas in the accumulation zone. (…) Without a consistent accumulation zone these glaciers are forecast not to survive the current climate or future additional warming. The results vary considerably with adjacent glaciers having a different survival forecast. This emphasizes the danger of extrapolating survival from one glacier to the next.

Viticultural effects

“With wine, we can taste climate change.” – Gregory V. Jones

“The result is that aromas lose their freshness, and the wines lack the delicate balance of acidity, sugar and tannins that allow them to age gracefully.” – AFP article on possible effects on Bordeaux wines

From 1950 to 1999 the majority of the world’s highest quality wine-producing regions experienced growing season warming trends. Vintage quality ratings during this same time period increased significantly while year-to-year variation declined. Currently, many European regions appear to be at or near their optimum growing season temperatures, while the relationships are less defined in the New World viticulture regions.

Historical evidence supports the connection between temperature and wine production where winegrape-growing regions developed when the climate was most conducive (Le Roy Ladurie, 1971; Pfister, 1988). Records of dates of harvest and yield for European viticulture have been kept for nearly a thousand years (Penning-Rowsell, 1989) revealing periods with more beneficial growing season temperatures and greater productivity. During the medieval “Little Optimum” period (roughly 900–1300 AD) vineyards were planted as far north as the coastal zones of the Baltic Sea and southern England, and during the High Middle Ages (12th and 13th centuries) harvesting occurred in early September as compared to early to mid October today (Pfister, 1988; Gladstones, 1992).

Here are some of the currently northernmost vineyards in Europe:

59°N is north of Scotland (Orkney Islands).

category: climate