Neil J. Holbrook

Evaluation of the AR4 Climate Models’ Simulated Daily Maximum Temperature, Minimum Temperature, and Precipitation over Australia Using Probability Density Functions

Abstract The coupled climate models used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change are evaluated. The evaluation is focused on 12 regions of Australia for the daily simulation of precipitation, minimum temperature, and maximum temperature. The evaluation is based on probability density functions and a simple quantitative measure of how well each climate model can capture the observed probability density functions for each variable and each region is introduced. Across all three variables, the coupled climate models perform better than expected. Precipitation is simulated reasonably by most and very well by a small number of models, although the problem with excessive drizzle is apparent in most models. Averaged over Australia, 3 of the 14 climate models capture more than 80% of the observed probability density functions for precipitation. Minimum temperature is simulated well, with 10 of the 13 climate models capturing more than 80% of the observed probability densit...

Impact of land cover change on the climate of southwest Western Australia

[1] A sudden reduction in rainfall occurred in the southwest of Western Australia in the mid-20th century. This reduced inflows to the Perth water supply by about 120 GL (42%) and led to an acceleration of projects to develop new water sources at a cost of about

Oceanic variability and coastal topography shape genetic structure in a long-dispersing sea urchin.

300 million. The reduction in rainfall was coincident with warmer temperatures. A major analysis of these changes indicated that the changes in temperature were likely caused by the enhanced greenhouse effect and that the changes in rainfall were likely caused by a large-scale reorganization of the atmospheric circulation. We explore an alternative hypothesis that large-scale land cover change explains the observed changes in rainfall and temperature. We use three high-resolution mesoscale model configurations forced at the boundaries to simulate (for each model) five July climates for each of natural and current land cover. We find that land cover change explains up to 50% of the observed warming. Following land cover change, we also find, in every simulation, a reduction in rainfall over southwest Western Australia and an increase in rainfall inland that matches the observations well. We show that the reduced surface roughness following land cover change largely explains the simulated changes in rainfall by increasing moisture divergence over southwest Western Australia and increasing moisture convergence inland. Increased horizontal wind magnitudes and suppressed vertical velocities over southwest Western Australia reduce the likelihood of precipitation. Inland, moisture convergence and increased vertical velocities lead to an increase in rainfall. Our results indicate that rainfall over southwest Western Australia may be returned to the long-term average through large-scale reforestation, a policy option within the control of local government. Such a program would also provide a century-scale carbon sink to ameliorate Australia’s very high per capita greenhouse gas emissions. INDEX TERMS: 1655 Global Change: Water cycles (1836); 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; 3329 Meteorology and Atmospheric Dynamics: Mesoscale meteorology; KEYWORDS: land cover change, mesoscale modeling, regional climate change

Assessing simulations of daily temperature and precipitation variability with global climate models for present and enhanced greenhouse climates

Understanding the scale of marine population connectivity is critical for the conservation and sustainable management of marine resources. For many marine species adults are benthic and relatively immobile, so patterns of larval dispersal and recruitment provide the key to understanding marine population connectivity. Contrary to previous expectations, recent studies have often detected unexpectedly low dispersal and fine-scale population structure in the sea, leading to a paradigm shift in how marine systems are viewed. Nonetheless, the link between fine-scale marine population structure and the underlying physical and biological processes has not been made. Here we show that patterns of genetic structure and population connectivity in the broadcast-spawning and long-distance dispersing sea urchin Centrostephanus rodgersii are influenced by physical oceanographic and geographic variables. Despite weak genetic differentiation and no isolation-by-distance over thousands of kilometers among samples from eastern Australia and northern New Zealand, fine-scale genetic structure was associated with sea surface temperature (SST) variability and geography along the southeastern Australian coast. The zone of high SST variability is characterized by periodic shedding of eddies from the East Australian Current, and we suggest that ocean current circulation may, through its influence on larval transport and recruitment, interact with the genetic consequences of large variance in individual reproductive success to generate patterns of fine-scale patchy genetic structure. If proven consistent across species, our findings suggest that the optimal scale for fisheries management and reserve design should vary among localities in relation to regional oceanographic variability and coastal geography.

Decadal climate variability in Australia during the twentieth century

The enhanced greenhouse climates of five different global climate models are examined with reference to the ability of the models to characterize the frequency of extreme events on both a regional and global scale. Ten years of model output for both control and enhanced greenhouse conditions are utilized to derive return periods for extreme temperature and precipitation events and to characterize the variability of the model climate at both regional and global scales. Under enhanced greenhouse conditions, return periods for extreme precipitation events are shorter and there is a general increase in the intensity of precipitation and number of wet spells in most areas. There is a decrease in frequency of cold temperature extremes and an increase in hot extremes in many areas. The results show a reasonable level of agreement between the models in terms of global scale variability, but the difference between model simulations of precipitation on a regional scale suggests that model derived estimates of variability changes must be carefully justified.

Interannual and decadal temperature variability in the Southwest Pacific Ocean between 1955 and 1988

High quality rainfall and surface temperature records for Australia during the period 1910–1993 are examined to quantify the relative importance of decadal variability and to ascertain if there is any relationship with sea-surface temperature (SST) variability over adjacent oceans on the same time scale. The decadal signal was estimated by low-pass filtering detrended annual averages of gridded data covering the entire continent to eliminate all spectral contributions with periods less than or equal to 8 years. Such variability typically accounts for 10–60% of the total variance. Low-pass filtering does not appear to affect the structure of the leading empirical orthogonal functions (EOFs) of rainfall and temperature, and the variability of all-Australia averages of these quantities are reasonably well-modeled as red noise, for which there is no preference for decadal time scales. Decadal variability in Indian Ocean SST south of 40°S is associated with rainfall variability over eastern Australia. A tendency for increased Tasman Sea SST (south of 15°S) to coincide with the above normal central and eastern Australian rainfall on both interannual and decadal time scales is also evident. The first EOF of interannual Pacific SST is associated with rainfall variability over Australia. This is not surprising as the EOF has an amplitude that tends to be out of phase with the Southern Oscillation Index (SOI). A similar relationship exists between the EOF of decadal SST variability and decadal fluctuations in both rainfall and the SOI. The first EOF of decadal Pacific SST has a broad spatial structure extending into the North and South Pacific. It has a time coefficient that is well-represented by the decadal component of the (northern) winter-time SST EOF produced in a separate study, which is available back to the turn of the century. When the decadal SST EOF warms the central Pacific, Australian rainfall is reduced, and both the daily maximum temperature and the diurnal temperature range over Australia are increased. These changes are consistent with radiative and evaporative changes associated with fluctuations in rainfall, cloud cover and soil moisture.

The Southwest Pacific Ocean circulation and climate experiment (SPICE)

Abstract The spatial and temporal variability of the southwest Pacific Ocean is examined with the aim of describing the physical processes operating on interannual and decadal timescales. The study takes advantage of a new temperature atlas of the upper 450 m of the southwest Pacific Ocean, obtained from 40 000 bathythermograph profiles between 1955 and 1988. Rotated principal components analysis was used to filter the important spatial and temporal scales of temperature variability in the data. Three different analyses are presented. They include two intraocean analyses and a joint analysis of subsurface ocean temperature, sea level pressure, and surface winds. The dominant El Nino mode describes the large vertical excursions of the thermocline in the western tropical Pacific in response to atmospheric forcing at a 3–6-month lag. More importantly, most of the retained modes, outside of the equatorial region, have time variations that correlate with El Nino. One ocean mode, with a spatial pattern represen...

The short history of research in a marine climate change hotspot: from anecdote to adaptation in south-east Australia

The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin-scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua-New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon, and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Nino-Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After 7 years of substantial in situ oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways, and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter-intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions.

A Poisson Regression Model of Tropical Cyclogenesis for the Australian–Southwest Pacific Ocean Region

Climate change is not being felt equally around the world. Regions where warming is most rapid will be among those to experience impacts first, will need to develop early responses to these impacts and can provide a guide for management elsewhere. We describe the research history in one such global marine hotspot—south-east Australia—where a number of contentions about the value of hotspots as natural laboratories have been supported, including (1) early reporting of changes (2) early documentation of impacts, and (3) earlier development and promotion of adaptation options. We illustrate a transition from single discipline impacts-focused research to an inter-disciplinary systems view of adaptation research. This transition occurred against a background of change in the political position around climate change and was facilitated by four preconditioning factors. These were: (1) early observations of rapid oceanic change that coincided with (2) biological change which together provided a focus for action, (3) the strong marine orientation and history of management in the region, and (4) the presence of well developed networks. Three case studies collectively show the critical role of inter-disciplinary engagement and stakeholder participation in supporting industry and government adaptation planning.

Interrogating resilience: toward a typology to improve its operationalization

Abstract This paper seeks to address some of the limitations in previous statistical forecast models of tropical cyclogenesis through the development of a series of Poisson regression models on a 2° latitude × 5° longitude spatial grid and a monthly grid in time. The “Gray” parameters [low-level relative vorticity, vertical wind shear parameter, ocean thermal energy, (saturated) equivalent potential temperature gradient, and middle-troposphere humidity] were analyzed as potential predictors of tropical cyclogenesis for the Australian–southwest Pacific Ocean region. Various predictor lead times of up to 5 months were investigated, with the most significant Poisson regression models being cross validated, and the skill of their hindcasts evaluated. The Poisson regression model incorporating a combination of saturated equivalent potential temperature gradients at various leads was found to be the most skillful in hindcasting the temporal (phase and amplitude) variability of tropical cyclogenesis for the Aust...