Expected impacts of climate change on extreme climate events

An overview of the expected change of climate extremes during this century due to greenhouse gases and aerosol anthropogenic emissions is presented. The most commonly used methodologies rely on the dynamical or statistical downscaling of climate projections, performed with coupled atmosphere–ocean general circulation models. Either of dynamical or of statistical type, downscaling methods present strengths and weaknesses, but neither their validation on present climate conditions, nor their potential ability to project the impact of climate change on extreme event statistics allows one to give a specific advantage to one of the two types. The results synthesized in the last IPCC report and more recent studies underline a convergence for a very likely increase in heat wave episodes over land surfaces, linked to the mean warming and the increase in temperature variability. In addition, the number of days of frost should decrease and the growing season length should increase. The projected increase in heavy precipitation events appears also as very likely over most areas and also seems linked to a change in the shape of the precipitation intensity distribution. The global trends for drought duration are less consistent between models and downscaling methodologies, due to their regional variability. The change of wind-related extremes is also regionally dependent, and associated to a poleward displacement of the midlatitude storm tracks. The specific study of extreme events over France reveals the high sensitivity of some statistics of climate extremes at the decadal time scale as a consequence of regional climate internal variability.     

The climate attractor

Time series of proxy data representing long-term variation of the terrestrial climate presumably show aperiodic changes, which has given rise to the hypothesis that the dynamics of the earth’s climate is governed by a strange attractor. Here a study of such attractors is presented, with emphasis on determination of its dimension and the reported results. Finally, a one dimensional delayed albedo feedback climate model is discussed with the related strange attractor and its dimension.     

Tectonics and climate

Tectonics and climate are both directly and indirectly related. The direct connection is between uplift, atmospheric circulation, and the hydrologic cycle. The indirect links are via subduction, volcanism, the introduction of gasses into the atmosphere, and through erosion and consumption of atmospheric gases by chemical weathering. Rifting of continental blocks involves broad upwarping followed by subsidence of a central valley and uplift of marginal shoulders. The result is an evolving regional climate which has been repeated many times in the Phanerozoic: first a vapor-trapping arch, followed by a rift valley with fresh-water lakes, culminating in an arid rift bordered by mountains intercepting incoming precipitation. Convergence tectonics affects climate on a larger scale. A mountain range is a barrier to atmospheric circulation, especially if perpendicular to the circulation. It also traps water vapor converting latent to sensible heat. Broad uplift results in a shorter path for both incoming and outgoing radiation resulting in seasonal climate extremes with reversals of atmospheric pressure and enhanced monsoonal circulation. Volcanism affects climate by introducing ash and aerosols into the atmosphere, but unless these are injected into the stratosphere, they have little effect. Stratospheric injection is most likely to occur at high latitudes, where the thickness of the troposphere is minimal. Volcanoes introduce CO₂, a greenhouse gas, into the atmosphere. Geochemical effects of tectonic uplift and unroofing relate to the weathering of silicate rocks, the means by which CO₂ is removed from the atmosphere-ocean system on long-term time scales.     

Fingerprinting the 8.2 ka event climate response in a coupled climate model

Using results from coupled climate model simulations of the 8.2 ka climate event that produced a cold period over Greenland in agreement with the reconstructed cooling from ice cores, we investigate the typical pattern of climate anomalies (fingerprint) to provide a framework for the interpretation of global proxy data for the 8.2 ka climate event. For this purpose we developed an analysis method that isolates the forced temperature response and provides information on spatial variations in magnitude, timing and duration that characterise the detectable climate event in proxy archives. Our analysis shows that delays in the temperature response to the freshwater forcing are present, mostly in the order of decades (30 a over central Greenland). The North Atlantic Ocean initially cools in response to the freshwater perturbation, followed in certain parts by a warm response. This delay, occurring more than 200 a after the freshwater pulse, hints at an overshoot in the recovery from the freshwater perturbation. The South Atlantic and the Southern Ocean show a warm response reflecting the bipolar seesaw effect. The duration of the simulated event varies for different areas, and the highest probability of recording the event in proxy archives is in the North Atlantic Ocean area north of 40° N. Our results may facilitate the interpretation of proxy archives recording the 8.2 ka event, as they show that timing and duration cannot be assumed to correspond with the timing and duration of the event as recorded in Greenland ice cores. Copyright © 2011 John Wiley & Sons, Ltd.     

Orbital changes and climate

At the 41,000-period of orbital tilt, summer insolation forces a lagged response in northern ice sheets. This delayed ice signal is rapidly transferred to nearby northern oceans and landmasses by atmospheric dynamics. These ice-driven responses lead to late-phased changes in atmospheric CO₂ that provide positive feedback to the ice sheets and also project ‘late’ 41-K forcing across the tropics and the Southern Hemisphere. Responses in austral regions are also influenced by a fast response to summer insolation forcing at high southern latitudes.At the 22,000-year precession period, northern summer insolation again forces a lagged ice-sheet response, but with muted transfers to proximal regions and no subsequent effect on atmospheric CO₂. Most 22,000-year greenhouse-gas responses have the ‘early’ phase of July insolation. July forcing of monsoonal and boreal wetlands explains the early CH₄ response. The slightly later 22-K CO₂ response originates in the southern hemisphere. The early 22-K CH₄ and CO₂ responses add to insolation forcing of the ice sheets.The dominant 100,000-year response of ice sheets is not externally forced, nor does it result from internal resonance. Internal forcing appears to play at most a minor role. The origin of this signal lies mainly in internal feedbacks (CO₂ and ice albedo) that drive the gradual build-up of large ice sheets and then their rapid destruction. Ice melting during terminations is initiated by uniquely coincident forcing from insolation and greenhouse gases at the periods of tilt and precession.     

On global climate warming

On global climate warming     

Circulating climate services: Commercializing science for climate change adaptation in Pacific Islands

In order to address the impacts of climate change, global multilateral institutions, development organizations, and national and regional science organizations are creating climate services – packages of useful climate information intended to help decision makers. This diffuse collection of actors and institutions suggest that producing climate services will help bridge gaps between climate scientists and decision-makers and will therefore help vulnerable countries and people manage the risks and optimize the impacts of climate change. This article examines this global science-policy ecosystem using the case of climate services produced by Australian science agencies for consumption in adaptation programming in the Pacific Island countries of Kiribati and Solomon Islands. Linking research on geographies of marketization and the neoliberalization of science, I demonstrate that within the climate service movement a focus on usefulness is paired with an emphasis on commercialization. As a result, this case shows the inherent tensions in the climate service model: first, a focus on competition and circulating service products at the expense of collaborative relationships; second, difficulties in negotiating uncertainty; and third contradictions between ‘objective’ and ‘entrepreneurial’ science. In each of these instances, the commercialized mechanisms through which climate services are governed, and the political economic circumstances within which they are produced, magnify rather than ameliorate gaps between science and policy.     

The Preboreal climate reversal and a subsequent solar‐forced climate shift

Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric ¹⁴C; (ii) a temporary decline of atmospheric CO₂; and (iii) an increase in the GRIP ¹⁰Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.     

Holocene climate of New England

Stratigraphic studies of pollen and macrofossils from six sites at different elevations in the White Mountains of New Hampshire demonstrate changes in the distributions of four coniferous tree species during the Holocene. Two species presently confined to low elevations extended farther up the mountain slopes during the early Holocene: white pine grew 350 m above its present limit beginning 9000 yr B.P., while hemlock grew 300–400 m above its present limit soon after the species immigrated to the region 7000 yr. B.P. Hemlock disappeared from the highest sites about 5000 yr B.P., but both species persisted at sites 50–350 m above their present limits until the Little Ice Age began a few centuries ago. The history of the two main high-elevation conifers is more difficult to interpret. Spruce and fir first occur near their present upper limits 9000 or 10,000 yr B.P. Fir persisted in abundance at elevations similar to those where it occurs today throughout the Holocene, while spruce became infrequent at all elevations from the beginning of the Holocene until 2000 yr B.P. These facts suggest a more complex series of changes than a mere upward shift of the modern environmental gradient. Nevertheless, we conclude that the minimum climatic change which would explain the upward extensions of hemlock and white pine is a rise in temperature, perhaps as much as 2°C. The interval of maximum warmth started 9000 yr B.P. and lasted at least until 5000 yr B.P., correlative with the Prairie Period in Minnesota.     

An overview of climate models

Climate models and results, especially for paleo-climatic scale are reviewed. It is concluded that the climatic system is more stable than it was thought to be when Budyko-Sellers type models first came into existence. Even a 2% decrease in solar radiation may not result in White Earth due to negative feed-backs. A decrease in CO₂ to about 200 ppm can result in White Earth. A doubling of CO₂ increases the surface temperature by an order of 1°C. The total climatic system which is nonlinear can exhibit very long period internal oscillations, even of the order of 1,00,000 years though none of the time constants involved are in that range individually.     

Mid-Holocene climate in Northern Minnesota

Study of Holocene ostracodes and diatoms from Elk Lake, in North-Central Minnesota, indicates that the local climate of the mid-Holocene can be subdivided into three intervals. Throughout interval 1 (ca. 7800 to 6700 yr B.P.), climate was colder and much drier than today. During intervals 2 and 3 (ca. 6700 to 4000 yr B.P.) average mean-annual air temperatures approached the modern mean (3.7°C), but warm summers persisted throughout interval 2, whereas during interval 3 warm summers fell into discrete episodes. Furthermore, average mean-annual precipitation was about 85 and 90% of modern during intervals 2 and 3, respectively. Transition times between the principal intervals were less than 50 yr. The expected effects of a retreating Laurentide Ice Sheet that initially maintained a winter-style circulation, followed by transitional climate states, and finally a near-modern circulation pattern may explain these local climatic events.     

Experiments in long-range climate control

Extrapolation of the palaeoclimate chronology of the past million years or so seems to leave little doubt that another glacial stage can be expected in the near geologic future. On a shorter time scale it appears that the increasing greenhouse effect from the use of fossil fuel will raise atmospheric temperature by 2 to 3 °K within a hundred years. The possibility of man's reversing or at least weakening these portentous climate changes is investigated here with the use of a thermodynamic climate model. Preliminary results indicate that the climate effects referred to may be reversible if caught early and certainly suggest that further and more sophisticated attention be given the subject.     

Coastal megacities and climate change

Rapid urbanization is projected to produce 20 coastal megacities (population exceeding 8 million) by 2010. This is mainly a developing world phenomenon: in 1990, there were seven coastal megacities in Asia (excluding those in Japan) and two in South America, rising by 2010 to 12 in Asia (including Istanbul), three in South America and one in Africa.All coastal locations, including megacities, are at risk to the impacts of accelerated global sea-level rise and other coastal implications of climate change, such as changing storm frequency. Further, many of the coastal megacities are built on geologically young sedimentary strata that are prone to subsidence given excessive groundwater withdrawal. At least eight of the projected 20 coastal megacities have experienced a local orrelative rise in sea level which often greatly exceeds any likely global sea-level rise scenario for the next century.The implications of climate change for each coastal megacity vary significantly, so each city requires independent assessment. In contrast to historical precedent, a proactive perspective towards coastal hazards and changing levels of risk with time is recommended. Low-cost measures to maintain or increase future flexibility of response to climate change need to be identified and implemented as part of an integrated approach to coastal management.     

Earth dynamics and climate changes

The evolution of the Earth's climate over geological time is now relatively well known. Conversely, the causes and feedback mechanisms involved in these climatic changes are still not well determined. At geological timescales, two factors play a prevailing role: plate tectonics and the chemical composition of the atmosphere. Their climatic effects will be examined using palaeoclimatic indicators as well as results of climate models. I focus primarily on the influence of continental drift on warm and cold climatic episodes. The consequences of peculiar land sea distributions (amalgamation/dispersal of continental blocks) are discussed. Plate tectonics also drive sea level changes as well as mountain uplift. Marine transgressions during the Mid-Cretaceous favoured warmth within the interiors of continents, although their effect could be very different according to the season. Mountain uplift is also an important factor, which is able to alter climate at large spatial scales. Experiments relative to climatic sensitivity to the elevation of the Appalachians during the Late Permian are discussed. To affect the whole Earth, the chemical composition of the atmosphere appears to be a more efficient forcing factor. The carbon dioxide driven by the long-term carbon cycle has influenced the global climate. Geochemical modelling simulates more or less accurately the long-term evolution of pCO₂, which corresponds roughly to the icehouse/greenhouse climatic oscillations. However, the uncertainties on pCO₂ are still important because different parameters involved in the long-term carbon cycle (degassing rate, chemical weathering of silicates, burial of organic matter) are not well constrained throughout the past. The chemical composition of the atmosphere is also altered by the emissions of modern volcanic eruptions leading to weak global cooling. The influence of large flood basalt provinces on climate is not yet known well enough; this volcanism may have released huge amounts of SO₂ as well as CO₂. At last, the chemical composition of the atmosphere may have been altered by the release of methane in response to the dissociation of gas hydrates. This scenario has been proposed to explain the abrupt warming during the Late Palaeocene.