Pattern Of Surface Warming Research Articles

Global Hydrological Cycle Response to Rapid and Slow Global Warming

AbstractThis study analyzes the response of global water vapor to global warming in a series of fully coupled climate model simulations. The authors find that a roughly 7% K−1 rate of increase of water vapor with global surface temperature is robust only for rapid anthropogenic-like climate change. For slower warming that occurred naturally in the past, the Southern Ocean has time to equilibrate, producing a different pattern of surface warming, so that water vapor increases at only 4.2% K−1. This lower rate of increase of water vapor with warming is not due to relative humidity changes or differences in mean lower-tropospheric temperature. A temperature of over 80°C would be required in the Clausius–Clapeyron relationship to match the 4.2% K−1 rate of increase. Instead, the low rate of increase is due to spatially heterogeneous warming. During slower global warming, there is enhanced warming at southern high latitudes, and hence less warming in the tropics per kelvin of global surface temperature increase. This leads to a smaller global water vapor increase, because most of the atmospheric water vapor is in the tropics. A formula is proposed that applies to general warming scenarios. This study also examines the response of global-mean precipitation and the meridional profile of precipitation minus evaporation and compares the latter to thermodynamic scalings. It is found that global-mean precipitation changes are remarkably robust between rapid and slow warming. Thermodynamic scalings for the rapid- and slow-warming zonal-mean precipitation are similar, but the precipitation changes are significantly different, suggesting that circulation changes are important in driving these differences.

Time-Varying Climate Sensitivity from Regional Feedbacks

Abstract The sensitivity of global climate with respect to forcing is generally described in terms of the global climate feedback—the global radiative response per degree of global annual mean surface temperature change. While the global climate feedback is often assumed to be constant, its value—diagnosed from global climate models—shows substantial time variation under transient warming. Here a reformulation of the global climate feedback in terms of its contributions from regional climate feedbacks is proposed, providing a clear physical insight into this behavior. Using (i) a state-of-the-art global climate model and (ii) a low-order energy balance model, it is shown that the global climate feedback is fundamentally linked to the geographic pattern of regional climate feedbacks and the geographic pattern of surface warming at any given time. Time variation of the global climate feedback arises naturally when the pattern of surface warming evolves, actuating feedbacks of different strengths in different regions. This result has substantial implications for the ability to constrain future climate changes from observations of past and present climate states. The regional climate feedbacks formulation also reveals fundamental biases in a widely used method for diagnosing climate sensitivity, feedbacks, and radiative forcing—the regression of the global top-of-atmosphere radiation flux on global surface temperature. Further, it suggests a clear mechanism for the “efficacies” of both ocean heat uptake and radiative forcing.

The roles of aerosol direct and indirect effects in past and future climate change

AbstractUsing the Geophysical Fluid Dynamics Laboratory's (GFDL's) fully coupled chemistry‐climate (ocean/atmosphere/land/sea ice) model (CM3) with an explicit physical representation of aerosol indirect effects (cloud‐water droplet activation), we find that the dramatic emission reductions (35%–80%) in anthropogenic aerosols and their precursors projected by Representative Concentration Pathway (RCP) 4.5 result in ~1 °C of additional warming and ~0.1 mm day−1of additional precipitation, both globally averaged, by the end of the 21st century. The impact of these reductions in aerosol emissions on simulated global mean surface temperature and precipitation becomes apparent by mid‐21st century. Furthermore, we find that the aerosol emission reductions cause precipitation to increase in East and South Asia by ~1.0 mm day−1through the second half of the 21st century. Both the temperature and the precipitation responses simulated by CM3 are significantly stronger than the responses previously simulated by our earlier climate model (CM2.1) that only considered direct radiative forcing by aerosols. We conclude that the indirect effects of sulfate aerosol greatly enhance the impacts of aerosols on surface temperature in CM3; both direct and indirect effects from sulfate aerosols dominate the strong precipitation response, possibly with a small contribution from carbonaceous aerosols. Just as we found with the previous GFDL model, CM3 produces surface warming patterns that are uncorrelated with the spatial distribution of 21st century changes in aerosol loading. However, the largest precipitation increases in CM3 are colocated with the region of greatest aerosol decrease, in and downwind of Asia.

Does Antarctic glaciation force migration of the tropical rain belt?

High-resolution (similar to 3-6 k.y.) upper ocean temperature and salinity estimates derived from planktic foraminiferal delta(18)O and Mg/Ca in Ocean Drilling Program (ODP) Site 1146 reveal stepwise changes in the precipitation-evaporation balance of the subtropical northwestern Pacific during the Middle Miocene (15.7 to 12.7 Ma). We attribute the punctuated pattern of surface warming and freshening following Antarctic ice growth episodes at 14.6, 14.2, 13.9, and 13.1 Ma to successive northward movements of the Intertropical Convergence Zone, implying high sensitivity of tropical rain belts to the interhemispheric temperature gradient driven by high-latitude climate. This dynamic interaction has implications for future warmer climate regimes with differential warming of the Northern Hemisphere, as it may lead to changes in the latitudinal penetration of tropical Pacific moisture over Southeast Asia.

SURVIVAL IN A CHANGING WORLD

![Figure][1] In August 2009, the International Union of Physiological Sciences (IUPS) held its 36th Congress in Kyoto in the same convention centre where the historic Kyoto Protocol was drawn up 12 years earlier. The symbolism of this coincidence was not missed by Malcolm Gordon, the Chair of

Changes to ENSO under CO2 Doubling in a Multimodel Ensemble

Abstract An EOF analysis is used to intercompare the response of ENSO-like variability to CO2 doubling in results from 15 coupled climate models assembled for the Intergovernmental Panel on Climate Change Fourth Assessment Report. Under preindustrial conditions, 12 of the 15 models exhibit ENSO amplitudes comparable to or exceeding that observed in the second half of the twentieth century. Under CO2 doubling, three of the models exhibit statistically significant (p < 0.1) increases in ENSO amplitude, and five exhibit significant decreases. The overall amplitude changes are not strongly related to the magnitude or pattern of surface warming. It is, however, found that ENSO amplitude decreases (increases) in models having a narrow (wide) ENSO zonal wind stress response and ENSO amplitude comparable to or greater than observed. The models exhibit a mean fractional decrease in ENSO period of about 5%. Although many factors can influence the ENSO period, it is suggested that this may be related to a comparable increase in equatorial wave speed through an associated speedup of delayed-oscillator feedback. Changes in leading EOF, characterized in many of the models by a relative increase in the amplitude of SST variations in the central Pacific, are in most cases consistent with effects of anomalous zonal and vertical advection resulting from warming-induced changes in SST.

Abrupt hydrographic changes in the equatorial Pacific and subtropical Atlantic from foraminiferal Mg/Ca indicate greenhouse origin for the thermal maximum at the Paleocene‐Eocene Boundary

The Paleocene‐Eocene Boundary (PEB) was marked by an extraordinary climatic event, hypothesized to originate from a large perturbation to the carbon cycle which fueled global warming, the rapid dissociation of oceanic methane hydrates. The pattern of surface warming interpreted from existing sea surface temperature records is not consistent with a greenhouse origin for this event, which would have fueled sea surface warming globally. Although oxygen isotope (δ18O)‐based reconstructions indicate polar warming, results for the tropics and subtropics are ambiguous because of uncertainties associated with interpreting planktonic foraminiferal δ18O. To remedy this, we have constructed high‐resolution temperature records based on Mg/Ca of multiple species of both surface and thermocline‐dwelling planktonic foraminifera across the PEB in the equatorial Pacific and subtropical Atlantic. During the carbon isotope excursion (CIE), surface temperatures increased by 3.5°–4°C and thermocline temperatures warmed by 3°C. Estimates of surface water and thermocline salinity based on paired Mg/Ca and δ18O data indicate a pattern of hydrographic changes in the equatorial and subtropical oceans that is different from previously proposed, with a more vigorous hydrologic cycle during warming. The pattern of warming and salinity changes are consistent with this being a greenhouse‐induced global warming event, and the timing of hydrographic changes relative to the CIE supports the hypothesis that gradual warming of intermediate/deep waters triggered methane hydrate dissociation.