Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

Climate phenomena and their relevance for future regional climate change

Spatial variations in sea surface temperature (SST) and rainfall changes over the tropics are investigated based on ensemble simulations for the first half of the twenty-first century under the greenhouse gas (GHG) emission scenario A1B with coupled ocean–atmosphere general circulation models of the Geophysical Fluid Dynamics Laboratory (GFDL) and National Center for Atmospheric Research (NCAR). Despite a GHG increase that is nearly uniform in space, pronounced patterns emerge in both SST and precipitation. Regional differences in SST warming can be as large as the tropical-mean warming. Specifically, the tropical Pacific warming features a conspicuous maximum along the equator and a minimum in the southeast subtropics. The former is associated with westerly wind anomalies whereas the latter is linked to intensified southeast trade winds, suggestive of wind–evaporation–SST feedback. There is a tendency for a greater warming in the northern subtropics than in the southern subtropics in accordance ...

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Global warming pattern formation: sea surface temperature and rainfall.

Four-year averages of 25-kilometer-resolution measurements of near-surface wind speed and direction over the global ocean from the QuikSCAT satellite radar scatterometer reveal the existence of surprisingly persistent small-scale features in the dynamically and thermodynamically important curl and divergence of the wind stress. Air-sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields, as are the influences of islands and coastal mountains. Ocean currents such as the Gulf Stream generate distinctive patterns in the curl field. These previously unresolved features have important implications for oceanographic and air-sea interaction research.

https://science.sciencemag.org/content/sci/303/5660/978.full.pdf

Satellite measurements reveal persistent small-scale features in ocean winds.

Global Warming Pattern Formation: Sea Surface Temperature and Rainfall

El Nino’s influence on the subtropical northwest (NW) Pacific climate increased after the climate regime shift of the 1970s. This is manifested in well-organized atmospheric anomalies of suppressed convection and a surface anticyclone during the summer (June–August) of the El Nino decay year [JJA(1)], a season when equatorial Pacific sea surface temperature (SST) anomalies have dissipated. In situ observations and ocean–atmospheric reanalyses are used to investigate mechanisms for the interdecadal change. During JJA(1), the influence of the El Nino–Southern Oscillation (ENSO) on the NW Pacific is indirect, being mediated by SST conditions over the tropical Indian Ocean (TIO). The results here show that interdecadal change in this influence is due to changes in the TIO response to ENSO. During the postregime shift epoch, the El Nino teleconnection excites downwelling Rossby waves in the south TIO by anticyclonic wind curls. These Rossby waves propagate slowly westward, causing persistent SST warmi...

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Decadal Shift in El Niño Influences on Indo–Western Pacific and East Asian Climate in the 1970s*

Using satellite data, we detected a wind wake trailing westward behind the Hawaiian Islands for 3000 kilometers, a length many times greater than observed anywhere else on Earth. This wind wake drives an eastward ocean current that draws warm water from the Asian coast 8000 kilometers away, leaving marked changes in surface and subsurface ocean temperature. Standing in the path of the steady trade winds, Hawaii triggers an air-sea interaction that provides the feedback to sustain the influence of these small islands over a long stretch of the Pacific Ocean.

https://science.sciencemag.org/content/sci/292/5524/2057.full.pdf

Far-Reaching Effects of the Hawaiian Islands on the Pacific Ocean-Atmosphere System

Dynamics of the seasonal cycle of sea surface height (SSH) in the South China Sea (SCS) are studied using observations as well as numerical and theoretical models. Seasonal variability of the SCS is interpreted in light of large-scale dynamics and Rossby waves. It is found that the seasonal cycle over most of the SCS basin is determined predominantly by the regional ocean dynamics within the SCS. The SSH variability is shown to be forced mainly by surface wind curl on baroclinic Rossby waves. Annual baroclinic Rossby waves cross the basin in less than a few months, leaving the upper ocean in a quasi-steady Sverdrup balance. An anomalous cyclonic (anticyclonic) gyre is generated in winter (summer) by the anomalous cyclonic (anticyclonic) wind curl that is associated with the northeasterly (southwesterly) monsoon. In addition, surface heat flux acts to enhance the wind-generated variability. The winter surface cooling (warming) cools (warms) the mixed layer especially in the central SCS, reducing (...

Regional Dynamics of Seasonal Variability in the South China Sea

El Nino–Southern Oscillation (ENSO) induces climate anomalies around the globe. Atmospheric general circulation model simulations are used to investigate how ENSO-induced teleconnection patterns during boreal winter might change in response to global warming in the Pacific–North American sector. As models disagree on changes in the amplitude and spatial pattern of ENSO in response to global warming, for simplicity the same sea surface temperature (SST) pattern of ENSO is prescribed before and after the climate warming. In a warmer climate, precipitation anomalies intensify and move eastward over the equatorial Pacific during El Nino because the enhanced mean SST warming reduces the barrier to deep convection in the eastern basin. Associated with the eastward shift of tropical convective anomalies, the ENSO-forced Pacific–North American (PNA) teleconnection pattern moves eastward and intensifies under the climate warming. By contrast, the PNA mode of atmospheric internal variability remains largely...

Global Warming–Induced Changes in El Niño Teleconnections over the North Pacific and North America

Low-frequency modulation and change under global warming of the Indian Ocean dipole (IOD) mode are investigated with a pair of multicentury integrations of a coupled ocean–atmosphere general circulation model: one under constant climate forcing and one forced by increasing greenhouse gas concentrations. In the unforced simulation, there is significant decadal and multidecadal modulation of the IOD variance. The mean thermocline depth in the eastern equatorial Indian Ocean (EEIO) is important for the slow modulation, skewness, and ENSO correlation of the IOD. With a shoaling (deepening) of the EEIO thermocline, the thermocline feedback strengthens, and this leads to an increase in IOD variance, a reduction of the negative skewness of the IOD, and a weakening of the IOD–ENSO correlation. In response to increasing greenhouse gases, a weakening of the Walker circulation leads to easterly wind anomalies in the equatorial Indian Ocean; the oceanic response to weakened circulation is a thermocline shoal...

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Qinyu Liu

Papers

Decadal Shift in El Niño Influences on Indo–Western Pacific and East Asian Climate in the 1970s*

Far-Reaching Effects of the Hawaiian Islands on the Pacific Ocean-Atmosphere System

Regional Dynamics of Seasonal Variability in the South China Sea

Global Warming–Induced Changes in El Niño Teleconnections over the North Pacific and North America

Indian Ocean Dipole Response to Global Warming: Analysis of Ocean–Atmospheric Feedbacks in a Coupled Model*