Future Sea Surface Temperature Research Articles

An empirical model for probabilistic decadal prediction: global attribution and regional hindcasts

Empirical models, designed to predict surface variables over seasons to decades ahead, provide useful benchmarks for comparison against the performance of dynamical forecast systems; they may also be employable as predictive tools for use by climate services in their own right. A new global empirical decadal prediction system is presented, based on a multiple linear regression approach designed to produce probabilistic output for comparison against dynamical models. A global attribution is performed initially to identify the important forcing and predictor components of the model . Ensemble hindcasts of surface air temperature anomaly fields are then generated, based on the forcings and predictors identified as important, under a series of different prediction ‘modes’ and their performance is evaluated. The modes include a real-time setting, a scenario in which future volcanic forcings are prescribed during the hindcasts, and an approach which exploits knowledge of the forced trend. A two-tier prediction system, which uses knowledge of future sea surface temperatures in the Pacific and Atlantic Oceans, is also tested, but within a perfect knowledge framework. Each mode is designed to identify sources of predictability and uncertainty, as well as investigate different approaches to the design of decadal prediction systems for operational use. It is found that the empirical model shows skill above that of persistence hindcasts for annual means at lead times of up to 10 years ahead in all of the prediction modes investigated. It is suggested that hindcasts which exploit full knowledge of the forced trend due to increasing greenhouse gases throughout the hindcast period can provide more robust estimates of model bias for the calibration of the empirical model in an operational setting. The two-tier system shows potential for improved real-time prediction, given the assumption that skilful predictions of large-scale modes of variability are available. The empirical model framework has been designed with enough flexibility to facilitate further developments, including the prediction of other surface variables and the ability to incorporate additional predictors within the model that are shown to contribute significantly to variability at the local scale. It is also semi-operational in the sense that forecasts have been produced for the coming decade and can be updated when additional data becomes available.

Prediction of interannual North Atlantic sea surface temperature and its remote influence over land

The quality of a multimodel of six coupled climate forecast systems initialized with observations—relative to the accompanying uninitialized system—to re-forecast the future annual-mean North Atlantic sea surface temperature (SST) departures is described. The study concludes that, measured by the anomaly correlation (AC) skill, the evolution of the leading two empirical orthogonal function modes of North Atlantic SSTs are skillfully forecast throughout the 9-year forecast range. This skill results in part from the predictions of the trend. The skill of the detrended modes, i.e., in absence of SST variability generated by the trend, is reduced, but still statistically distinguishable from zero throughout the 9-year forecast for the first mode and exclusively in the first two forecast years for the second mode. The initialization effect on the AC skill in the initialized system is statistically distinguishable from the one without initialization for the detrended first mode during the first three forecast years and the first forecast year only when the trend in North Atlantic SSTs is included. All six initialized systems of the multimodel are capable to skillfully forecast the shift of the full first mode of North Atlantic SST anomalies in the mid 1990s at all leads with HadCM 3 and EC-Earth 2.3 outperforming other systems. All systems share an intrinsic bias in simulating annual-mean SST variability in the North Atlantic. The study finds that the area-average AC skill (i.e., of a forecast containing regional information) of the North Atlantic influence on anomalous European temperature in the initialized multimodel is positive and statistically distinguishable from zero throughout the 9-year forecast for the full field case. On the other hand, a continent-wide forecast (i.e., without any regional information) of future European precipitation departures associated with North Atlantic SST variability is skillful throughout the 9-year forecast for the full field case—once the model remote influence is corrected by the observed. For the detrended case, the forecasts of the influence of the North Atlantic SSTs on both interannual temperature and precipitation departures in Europe show residual skill—which means that the multimodel is able to predict part of them beyond the trend. However, the forecasts of the North Atlantic influence on precipitation departures in the Sahel turn out not to be skillful.

Future Projections of Extreme Ocean Wave Climates and the Relation to Tropical Cyclones: Ensemble Experiments of MRI-AGCM3.2H*

Abstract Future projections of extreme ocean surface wave climates were carried out with single-model ensemble experiments of the atmospheric global climate model MRI-AGCM3.2H. The ensemble experiments of MRI-AGCM3.2H consist of four future sea surface temperature (SST) ensembles and three perturbed physics (PP) ensembles. This study showed that future changes in extreme wave heights strongly depend on the global climate model (GCM) performance to simulate tropical cyclones (TCs), indicating a need to acknowledge that results in a study that employs a low-performance model are not able to account for extreme waves associated with TCs (TC waves). The spatial distribution of future changes in non-TC extreme wave heights on the global scale was similar to that for mean wave heights; namely, wave heights increase over the middle-to-high latitudes in the Southern Ocean and central North Pacific and decrease over midlatitudes and the North Atlantic, although the magnitude of future changes for extreme wave heights is greater than for mean wave heights. The variance of future changes mainly depends on differences in physics among PP ensemble experiments rather than differences in SST ensembles. The 10-yr return wave heights of TC waves over the western North Pacific showed either an increase or a decrease of 30% for different regions, maximally. The spatial distribution of future changes in TC waves can be explained by an eastward shift of TC tracks.

Looking back and looking forwards: Historical and future trends in sea surface temperature (SST) in the Indo-Pacific region from 1982 to 2100

The ocean warming trend is a well-known global phenomenon. As early as 2001, and then reiterated in 2007, the Intergovernmental Panel on Climate Change (IPCC) reported that the global average sea surface temperature (SST) will increase by about 0.2°C per decade. To date, however, only a limited number of studies have been published reporting the spatio-temporal trends in SST in the Indo-Pacific region, one the richest marine ecosystems on Earth. In this research, the monthly 1° spatial resolution NOAA Optimum Interpolation (OI) sea surface temperature (SST) V2 dataset (OISSTv2) derived from measurements made by the Advanced Very High Resolution Radiometer (AVHRR) and in situ measurements, were used to examine the spatio-temporal trends in SST in the region. The multi-model mean SST from the Representative Concentration Pathways (RCP2.6) mitigation scenario of the Coupled Model Intercomparison Project Phase 5 (CMIP5) was also used to forecast future SST from 2020 to 2100, decadally. Three variables from the OISSTv2, namely maximum (MaxSST), mean (MeanSST) and minimum (MinSST) monthly mean SST, were regressed against time measured in months from 1982 to 2010 using linear regression. Results revealed warming trends detected for all three SST variables. In the Coral Triangle a warming trend with a rate of 0.013°C year−1, 0.017°C year−1, and 0.019°C year−1 was detected over 29 years for MaxSST, MeanSST and MinSST, respectively. In the SCS, the warming rate was 0.011°C year−1, (MaxSST), 0.012°C year−1 (MeanSST) and 0.015°C year−1 (MinSST) over 29 years. The CMIP5 RCP2.6 forecast suggested a future warming rate to 2100 of 0.004°C year−1 for both areas, and for all three SST variables. The warming trends reported in this study provide useful insights for improved marine-related management.

Present-day and future climate pathways affecting Alexandrium blooms in Puget Sound, WA, USA

This study uses a mechanistic modeling approach to evaluate the effects of various climate pathways on the proliferative phase of the toxin-producing dinoflagellate Alexandrium in Puget Sound, WA, USA. Experimentally derived Alexandrium growth responses to temperature and salinity are combined with simulations of the regional climate and Salish Sea hydrology to investigate future changes in the timing, duration, and extent of blooms. Coarse-grid (100–200km) global climate model ensemble simulations of the SRES A1B emissions scenario were regionally downscaled to a 12-km grid using the Weather Research and Forecasting model for the period 1969–2069. These results were used to: (1) analyze the future potential changes and variability of coastal upwelling winds, and (2) provide forcing fields to a Regional Ocean Model System used to simulate the circulation of the Salish Sea, including Puget Sound, and the coastal ocean. By comparing circa-1990 and circa-2050 climate scenarios for the environmental conditions that promote Alexandrium blooms, we disentangle the effects of three climate pathways: (1) increased local atmospheric heating, (2) changing riverflow magnitude and timing, and (3) changing ocean inputs associated with changes in upwelling-favorable winds. Future warmer sea surface temperatures in Puget Sound from increased local atmospheric heating increase the maximum growth rates that can be attained by Alexandrium during the bloom season as well as the number of days with conditions that are favorable for bloom development. This could lead to 30 more days a year with bloom-favorable conditions by 2050. In contrast, changes in surface salinity arising from changes in the timing of riverflow have a negligible effect on Alexandrium growth rates, and the behavior of the coastal inputs in the simulations suggests that changes in local upwelling will not have major effects on sea surface temperature or salinity or Alexandrium growth rates in Puget Sound.

Funding climate adaptation strategies with climate derivatives

Climate adaptation requires large capital investments that could be provided not only by traditional sources like governments and banks, but also by derivatives markets. Such markets would allow two parties with different tolerances and expectations about climate risks to transact for their mutual benefit and, in so doing, finance climate adaptation. Here we calculate the price of a derivative called a European put option, based on future sea surface temperature (SST) in Tasmania, Australia, with an 18°C strike threshold. This price represents a quantifiable indicator of climate risk, and forms the basis for aquaculture industries exposed to the risk of higher SST to finance adaptation strategies through the sale of derivative contracts. Such contracts provide a real incentive to parties with different climate outlooks, or risk exposure to take a market assessment of climate change.

The robustness of the atmospheric circulation and precipitation response to future anthropogenic surface warming

The impact of long-term sea surface temperature (SST) change on the atmospheric circulation is studied by comparing atmospheric general circulation model (AGCM) simulations forced with a spatially uniform SST increase and a structured SST increase. The structured SST increase is calculated from the response of an ensemble of coupled ocean-atmosphere models to increased CO2. Most of the impact of SST pattern change is confined to equatorial Indo-Pacific. However, the circulation change under the two types of SST forcing is similar over the rest of the tropics and almost identical in the extratropics, indicating that the pattern of future SST change has overall little impact on the response of the atmospheric circulation and, in turn, on the resulting changes in precipitation. The tropical similarity is argued to result from energetic constraints that weaken the atmospheric circulation, whereas the extratropical similarity likely results from the insensitivity of Rossby Wave generation to the changes in near-equatorial upper level divergence. A comparison of the AGCM simulations with those from externally forced coupled ocean-atmosphere models suggest that ocean coupling or the direct effect of radiative forcing has a larger impact on the projected changes in circulation and precipitation than the pattern of SST change over most regions.

Projected coral bleaching in response to future sea surface temperature rises and the uncertainties among climate models

We quantitatively evaluated the effects of rising sea surface temperature (SST) on coral bleaching and the uncertainties resulting from differences in global warming projections. To do so, we used monthly SSTs in the twenty-first century obtained from 23 climate models under the A1B scenario (from the Special Report on Emissions Scenarios) and SST-based indices for coral bleaching. All of the projections indicated that severe bleaching or death of corals will be common and severe in wide areas of the tropical and subtropical oceans by the middle of this century. However, decadal oscillation could modify the exact timing by around ±10 years. Such projections are important for conserving marine biodiversity and designing future strategies to avoid tropical and subtropical coral extinction. To obtain more reliable projections and reduce uncertainties, climate models should be improved by using higher spatiotemporal resolutions, and more realistic biological indices should be embedded into existing models.

Multi-Sensor Calibration Studies of AVHRR-Heritage Channel Radiances Using the Simultaneous Nadir Observation Approach

The European Space Agency project for studies of cloud properties in the Climate Change Initiative programme (ESA-CLOUD-CCI) aims at compiling the longest possible time series of cloud products from one single multispectral sensor—The five-channel Advanced Very High Resolution Radiometer (AVHRR) instrument. A particular aspect here is to include corresponding products based on other existing (Moderate Resolution Imaging Spectroradiometer (MODIS), Advanced Along-Track Scanning Radiometer (AATSR), MEdium Resolution Imaging Spectrometer (MERIS), Visible and Infrared Radiometer Suite (VIIRS)) and future Sea and Land Surface Temperature Radiometer (SLSTR) sensors measuring in similar (AVHRR-heritage) spectral channels. Initial inter-comparisons of the involved AVHRR-heritage channel radiances over a short demonstration period (2007–2009) were performed. Using Aqua-MODIS as reference, AVHRR (NOAA-18), AATSR, and MERIS channel radiances were evaluated using the simultaneous nadir (SNO) approach. Results show generally agreeing radiances within approximately 3% for channels at 0.6 µm and 0.8 µm. Larger deviations (+5%) were found for the corresponding AATSR channel at 0.6 µm. Excessive deviations but with opposite sign were also indicated for AATSR 1.6 µm and MERIS 0.8 µm radiances. Observed differences may largely be attributed to residual temporal and spatial matching differences while excessive AATSR and MERIS deviations are likely partly attributed to incomplete compensation for spectrally varying surface and atmospheric conditions. However, very good agreement was found for all infrared channels among all the studied sensors. Here, deviations were generally less than 0.2% for the measured brightness temperatures with the exception of some remaining non-linear deviations at extreme low and high temperatures.

Spatio‐temporal marine conservation planning to support high‐latitude coral range expansion under climate change

AbstractAimIncreasing sea‐surface temperatures (SST) have resulted in poleward range expansions of scleractinian corals and declines in their core ranges. These changes may provide management opportunities for the long‐term persistence of corals, but spatial prioritization rarely considers and anticipates these changes. We developed a spatio‐temporal conservation plan that accommodates future coral range expansions based on projections of futureSST. Our spatial planning approach is particularly useful in places with limited information about species distributions. Our aims were to (1) identify areas that consistently remain important for conservation through time and (2) determine the differences between priorities for conservation that account for potential coral range expansions and those that ignore them.LocationJapan.MethodsWe developed spatial planning approaches using predicted coral habitat distributions for current conditions, the near future and the distant future. Using theMarxan conservation planning software, we designed conservation plans for scenarios that incorporated different types of spatial and temporal connections. Spatial connections are physical connections between adjacent and nearby areas, whereas temporal connections connect planning areas throughout time.ResultsWe found that protecting areas important for current and future coral habitat distributions is possible by prioritizing places that are consistently important through time. A spatially and temporally cohesive plan was accomplished with only a 14% increase in the overall reserve system costs, compared with reserve systems ignoring future coral habitat distributions. The attributes of priority areas (e.g. locations, outside boundary length and size) were substantially different when we varied the types of connections.Main conclusionsThis study demonstrated that areas with highest conservation priority now will not necessarily be optimal when planning for future change, such as coral range expansions. Furthermore, we showed that incorporating spatio‐temporal connections into spatial prioritization achieves objectives of simultaneously conserving corals in the current climate and facilitating their expansions asSSTrises.

Rotating radiative‐convective equilibrium simulated by a cloud‐resolving model

The results of a series of cloud‐resolving radiative‐convective equilibrium (RCE) simulations are presented. The RCE simulations, used as an idealization for the mean tropical climate, are run for a wide range of prescribed sea‐surface temperatures (SSTs), from 21oC to 36oC, representing the range of past, present, and, possibly, future mean tropical SSTs. The RCE with constant Coriolis parameter f is contrasted with nonrotating RCE. The Coriolis parameter is artificially increased from typical values in the Tropics by about one order of magnitude to allow multiple tropical cyclones (TCs) to coexist in a relatively small 2300 × 2300 km2 domain with a 3 km horizontal grid spacing. Nonrotating RCE is also simulated, but using a substantially smaller, 384 × 384 km2 domain. Rotating RCE, which we nickname “TC World,” contains from 8 to 26 TCs with the average number of TCs monotonically decreasing with increasing SST. At the same time, the TCs' size, intensity, and per‐TC precipitation rate tend to increase in response to increasing SST. For example, the average per‐TC kinetic energy and precipitation rate tend to double for every 6oC SST increase. These results are consistent with scaling laws in which TC velocities and inner core diameters scale with the potential intensity and its ratio to the Coriolis parameter, respectively, while the separation between cyclone centers appears to scale with the deformation radius. It is also found that the outflow temperature of TC's, as defined as the height of the local maximum of the upper‐troposphere cloud fraction, remains relatively invariant with SST. The cold‐point tropopause height in TC World is found to be about 2 km higher than the corresponding height in nonrotating RCE.

Impacts of near future sea surface pH and temperature conditions on fertilisation and embryonic development in Centrostephanus rodgersii from northern New Zealand and northern New South Wales, Australia

Oceans are warming and becoming more acidic. While higher temperature and lower pH can have negative effects on fertilisation and development of marine invertebrates, warming may partially ameliorate the negative effect of lower pH. This study determined the effect of warming (3 °C) and decreased pH (0.3, 0.5, 1.1 units below ambient) on fertilisation and development in two populations of the sea urchin Centrostephanus rodgersii, one at its northern range limit (Coffs Harbour, New South Wales NSW, 30°27′S, 153°14′E) and the other one in New Zealand where the species may be a recent arrival (Mokohinau Islands, 35°56′S, 175°9′E). Both populations were sampled in August 2011. The two populations exhibited a differential response to temperature, while pH affected them similarly. Fertilisation was robust to pH levels forecast for 2100, and it was only slightly reduced at pH values forecast for 2300 (i.e. ≈5 and ≈8 % for the northern NSW and the New Zealand populations, respectively). Decreased pH (pH = 7.6) reduced the percentage of succeeding developmental stages. Progression through cleavage and hatching stages was faster at +3 °C in the New Zealand population but not in northern NSW urchins, while for the NSW population, there was a positive interaction between temperature and pH at hatching. Gastrulation was negatively affected by an extreme pH 7.0 treatment (60–80 % reduction) and least affected by increased temperature. The percentage of abnormal embryos at gastrulation increased significantly at +3 °C treatment in the northern NSW population. Predicted future increases in temperature may facilitate further expansion of the geographical range of C.rodgersii in New Zealand, with a minimal effect of concurrent reduced pH.

Future sea surface temperatures in Large Marine Ecosystems of the Northwest Atlantic

Abstract Khan, A. H., Levac, E., and Chmura, G. L. 2013. Future sea surface temperatures in Large Marine Ecosystems of the Northwest Atlantic. – ICES Journal of Marine Science, 70: 915–921. We analysed projections of future sea surface temperatures (SSTs) for six Large Marine Ecosystems (LMEs) of the Northwest Atlantic: the West Greenland Shelf, the Newfoundland-Labrador Shelf, the Scotian Shelf, the Northeast US continental shelf, the Southeast US continental shelf, and the Gulf of Mexico. We used state-of-the-art global climate models (CSIRO-Mk3.6, GISS-E2-R) and earth system models (CanESM2, HadGEM2-ES) and representative concentration pathways (RCPs) 8.5 and 4.5 that represent a range in possible future concentrations of atmospheric CO2. Our analysis focuses on average February and August SSTs from the period 2071–2100 as the low and high temperatures of these months generally define the thermal habitat of a species. SSTs will increase in most, but not all, waters of the LMEs, and seasonality will increase in all LMEs. The difference in SSTs from the Gulf of Mexico to the Scotian Shelf may be reduced but differences will increase from the Scotian Shelf north. Although past SST changes have been greatest on the Newfoundland-Labrador Shelf, ensemble average projections indicate that the greatest future change will occur on the Scotian Shelf. The variation in future SSTs is greater among models than between RCPs, suggesting that impact studies limited to a single model may be biased.

Typhoon and storm surge intensity changes in a warming climate around the Korean Peninsula

This study investigates the intensity change in typhoons and storm surges surrounding the Korean Peninsula under global warming conditions as obtained from the MPI_ECHAM5 climate model using the A1B series. The authors use the Cyclostationary Empirical Orthogonal Function to estimate future background fields for typhoon simulations from twenty-first-century prediction results. A series of numerical experiments applies WRF (Weather Research and Forecasting) and POM (Prinston Ocean Model) models to simulate two historical typhoons, Maemi (2003) and Rusa (2002), and associated storm surges under real historical and future warming conditions. Applying numerical experiments to two typhoons, this study found that their central pressure dropped about 19 and 17 hPa, respectively, when considering the future sea surface temperature (a warming of 3.9 °C for 100 years) over the East China Sea (Exp. 1). The associated enhancement of storm surge height ranged from 16 to 67 cm along the southern coast of the Korean Peninsula. However, when the study considered global warming conditions for other atmospheric variables such as sea-level pressure, air temperature, relative humidity, geopotential height, and wind in the typhoon simulations (Exp. 2), the intensities of the two typhoons and their associated surge heights scarcely increased compared to the results of Exp. 1. Analyzing projected atmospheric variables, the authors found that air temperatures at the top of the storm around 200 hPa increased more than those at the surface in tropical and mid-latitudes. The reduced vertical temperature difference provided an unfavorable condition in the typhoon’s development even under conditions of global warming. This suggests that global warming may not always correlate with a large increase in the number of intense cyclones and/or an increase in associated storm surges.

The Effects of Changes in Sea Surface Temperature and CO2 Concentration on the Quasi-Biennial Oscillation

Abstract The effects of sea surface temperature (SST) and CO2 on future changes in the quasi-biennial oscillation (QBO) are investigated using a climate model that simulates the QBO without parameterized nonstationary gravity wave forcing. Idealized model experiments using the future SST with the present CO2 (FS run) and the present SST with the future CO2 (FC run) are conducted, as are experiments using the present SST with the present CO2 (present run) and the future SST with the future CO2 (future run). When compared with the present run, precipitation increases around the equatorial region in the FS run and decreases in the FC run, resulting in increased and decreased wave momentum fluxes, respectively. In the midlatitude lower stratosphere, westward (eastward) wave-forcing anomalies form in the FS (FC) run. In the middle stratosphere off the equator, westward wave-forcing anomalies form in both the FS and FC runs. Corresponding to these wave-forcing anomalies, the residual vertical velocity significantly increases in the lower stratosphere in the FS run but decreases to below 70 hPa in the FC run, whereas residual upward circulation anomalies form in both the FS and FC runs in the middle equatorial stratosphere. Consequently, the amplitude of the QBO becomes smaller in the lower stratosphere, and the period of the QBO becomes longer by about 1–3 months in the FS run. On the other hand, in the FC run, the QBO extends farther downward into the lowermost stratosphere, and the period becomes longer by 1 month.

Increase of global monsoon area and precipitation under global warming: A robust signal?

Monsoons, the most energetic tropical climate system, exert a great social and economic impact upon billions of people around the world. The global monsoon precipitation had an increasing trend over the past three decades. Whether or not this increasing trend will continue in the 21st century is investigated, based on simulations of three high‐resolution atmospheric general circulation models that were forced by different future sea surface temperature (SST) warming patterns. The results show that the global monsoon area, precipitation and intensity all increase consistently among the model projections. This indicates that the strengthened global monsoon is a robust signal across the models and SST patterns explored here. The increase of the global monsoon precipitation is attributed to the increases of moisture convergence and surface evaporation. The former is caused by the increase of atmospheric water vapor and the latter is due to the increase of SST. The effect of the moisture and evaporation increase is offset to a certain extent by the weakening of the monsoon circulation.

Change and stasis in marine hybrid zones in response to climate warming

AbstractAim We test the prediction that hybrid zones between warm‐ and cold‐adapted species will move towards the territory formerly occupied by the cold‐adapted species in response to a warming climate. We use multiple tests of this prediction to distinguish amongst potential mechanistic hypotheses of responses to climate change.Location We sampled 97 locations on the Atlantic coast of Spain and France and the English Channel that span three hybrid zones formed between two species of marine mussels (Mytilus galloprovincialis and M. edulis).Methods Mussels were sampled in 2005–07 and analysed at a nuclear gene (Glu‐5′) that is diagnostically differentiated between the subject species. Results were compared to those of studies made in the same region over the past two decades. Historical change in sea surface temperature (SST) was analysed using National Oceanic and Atmospheric Administration (NOAA) Optimum Interpolation Daily SST. Species distribution models (random forest and maximum entropy) of the current distribution of mussels were constructed and validated by hindcasting the historical distributions of these species. Validated models were used in combination with forecasts of SST to predict changes in mussel distribution to 2050 and 2100.Results We show that over the past two decades two of the hybrid zones in France have not changed in either position or shape. The third hybrid zone, however, has shifted in the predicted direction, c. 100 km eastward into the warming English Channel. Species distribution modelling strongly implicates changes in winter cold SST as driving this change in the position of one of the hybrid zones. Forecasts of future SST indicate that rapid changes in distribution will occur over the next century.Main conclusions Hybrid zones can be used to conduct repeated tests of ecological responses to climate change and can be valuable in sorting among prospective mechanistic hypotheses that underlie that change. Winter temperatures, but not seasonal high temperature, appear to control the distribution of both species. Species distribution modelling indicates that the collapse of these hybrid zones is imminent, with the rapid expansion of the subtropical species in response to continuing SST warming.

Future changes in tropical cyclone activity projected by multi-physics and multi-SST ensemble experiments using the 60-km-mesh MRI-AGCM

Uncertainties in projected future changes in tropical cyclone (TC) activity are investigated using future (2075–2099) ensemble projections of global warming under the Intergovernmental Panel on Climate Change (IPCC) A1B scenario. Twelve ensemble experiments are performed using three different cumulus convection schemes and four different assumptions for prescribed future sea surface temperatures (SSTs). All ensemble experiments consistently project significant reductions in global and hemispheric TC genesis numbers as well as reductions in TC frequency of occurrence (TCF) and TC genesis frequency (TGF) in the western North Pacific, South Indian Ocean, and South Pacific Ocean. TCF and TGF are projected to increase over the central Pacific which is consistent with the findings of Li et al. (2010). Inter-experimental variations of projected future changes in TGF and TC genesis number are caused mainly by differences in large-scale dynamical parameters and SST anomalies. Thermodynamic parameters are of secondary importance for variations in TGF and TC genesis number. These results imply that differences in SST spatial patterns can cause substantial variations and uncertainties in projected future changes of TGF and TC numbers at ocean-basin scales.

Recent and future sea surface temperature trends in tropical pacific warm pool and cold tongue regions

Using coral data, sea surface temperature (SST) reanalysis data, and Climate Model Intercomparison Project III (CMIP3) data, we analyze 20th-century and future warm pool and cold tongue SST trends. For the last 100 years, a broad La Nina-like SST trend, in which the warming trend of the warm pool SST is greater than that of the cold tongue SST, has appeared in reanalysis SST data sets, 20C scenario experiments of the CMIP3 data and less significantly in coral records. However, most Coupled General Circulation Models subjected to scenarios of future high greenhouse gas concentrations produce larger SST warming trends in cold tongues than in warm pools, resembling El Nino-like SST patterns. In other words, warmer tropical climate conditions correspond to stronger El Nino-like response. Heat budget analyses further verify that warmer tropical climates diminish the role of the ocean’s dynamic thermostat, which currently regulates cold tongue temperatures. Therefore, the thermodynamic thermostat, whose efficiency depends on the mean temperature, becomes the main regulator (particularly via evaporative cooling) of both warm pool and cold tongue temperatures in future warm climate conditions. Thus, the warming tendency of the cold tongue SST may lead that of the warm pool SST in near future.

Future Change of Western North Pacific Typhoons: Projections by a 20-km-Mesh Global Atmospheric Model*

Abstract Projected future changes in tropical cyclone (TC) activity over the western North Pacific (WNP) under the Special Report on Emissions Scenarios (SRES) A1B emission scenario were investigated using a 20-km-mesh, very-high-resolution Meteorological Research Institute (MRI)–Japan Meteorological Agency (JMA) atmospheric general circulation model. The present-day (1979–2003) simulation yielded reasonably realistic climatology and interannual variability for TC genesis frequency and tracks. The future (2075–99) projection indicates (i) a significant reduction (by about 23%) in both TC genesis number and frequency of occurrence primarily during the late part of the year (September–December), (ii) an eastward shift in the positions of the two prevailing northward-recurving TC tracks during the peak TC season (July–October), and (iii) a significant reduction (by 44%) in TC frequency approaching coastal regions of Southeast Asia. The changes in occurrence frequency are due in part to changes in large-scale steering flows, but they are due mainly to changes in the locations of TC genesis; fewer TCs will form in the western portion of the WNP (west of 145°E), whereas more storms will form in the southeastern quadrant of the WNP (10°–20°N, 145°–160°E). Analysis of the genesis potential index reveals that the reduced TC genesis in the western WNP is due mainly to in situ weakening of large-scale ascent and decreasing midtropospheric relative humidity, which are associated with the enhanced descent of the tropical overturning circulation. The analysis also indicates that enhanced TC genesis in the southeastern WNP is due to increased low-level cyclonic vorticity and reduced vertical wind shear. These changes appear to be critically dependent on the spatial pattern of future sea surface temperature; therefore, it is necessary to conduct ensemble projections with a range of SST spatial patterns to understand the degree and distribution of uncertainty in future projections.