Purpose of Review The intertropical convergence zone (ITCZ) is a planetary-scale band of heavy precipitation close to the equator. Here, we consider the response of the ITCZ structure to climate change using observations, simulations, and theory. We focus on the substantial yet underappreciated projected changes in ITCZ width and strength, and highlight an emerging conceptual framework for understanding these changes. Recent FindingsSatellite observations and reanalysis data show a narrowing and strengthening of precipitation in the ITCZ over recent decades in both the Atlantic and Pacific basins, but little change in ITCZ location. Consistent with observations, coupled climate models predict no robust change in the zonal-mean ITCZ location over the twenty-first century. However, the majority of models project a narrowing of the ITCZ and weakening mean ascent. Interestingly, changes in ITCZ width and strength are strongly anti-correlated across models.Summary The ITCZ has narrowed over recent decades yet its location has remained approximately constant. Climate models project further narrowing and a weakening of the average ascent within the ITCZ as the climate continues to warm. Following intense work over the last ten years, the physical mechanisms controlling the ITCZ location are now well understood. The development of complementary theories for ITCZ width and strength is a current research priority. Outstanding challenges include understanding the ITCZ response to past climate changes and over land versus ocean regions, and better constraining all aspects of the ITCZ structure in model projections.

An objective, automated Intertropical Convergence Zone (ITCZ) identification and characterization algorithm is developed and applied to European Centre for Medium-Range Weather Forecasts Reanalysis Interim (ERA-Interim) variables, and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Global Precipitation Climatology Project (GPCP) rain rates (RRs) to create 15 and 36 year climatologies, respectively, in the tropical Pacific ocean. Characteristics derived from the algorithm include ITCZ latitude, northern and southern ITCZ convection boundaries and extent, and precipitation intensity. The climatological location of the ITCZ was found near 8 ∘ N, consistent with previous studies, with a preferred southern boundary location of 4 ∘ N. The northern ITCZ boundary did not exhibit a preferred boundary with locations between 7 ∘ and 15 ∘ N having similar frequencies of occurrence. The northern and southern extents of the ITCZ were symmetric in the central Pacific and asymmetric in the east Pacific. Long-term trends in the ITCZ width and precipitation intensity showed significant narrowing and intensifying. Separation of characteristics by season and location (i.e., central and eastern Pacific) revealed negative trends in ITCZ width in both domains, with trends in the east Pacific weaker than those in the central Pacific. Trends in precipitation intensity near the center of the ITCZ indicate a strong intensification, with slightly stronger trends in the central Pacific than in the east Pacific. These findings show that while the location of the ITCZ has not changed significantly over the past three decades, the ITCZ has narrowed and convection has intensified.

Many recent studies have aimed to better understand changes in the characteristics of the intertropical convergence zone (ITCZ), including ITCZ location, width, and precipitation intensity. However, very few studies have looked at the relationship between characteristics of convection within the ITCZ and ITCZ width. The present work uses information from an ITCZ identification database and Tropical Rainfall Measuring Mission (TRMM) precipitation feature (PF) database to quantify variations in convective characteristics across the ITCZ in the Pacific Ocean. Data are partitioned into wide and narrow ITCZ regimes to quantify differences in convection between different ITCZ regimes. Under the wide regime, convection deeper than 5 km, with areas greater than 100 km 2 , or stratiform rain fractions greater than 0.5 is, on average, 24%, 23%, and 12% more frequent, respectively. In the narrow regime, the signal is reversed, with average increases in the frequency of convection with heights below 5 km, areas less than 100 km 2 , or stratiform rain fractions less than 0.5 of 15%, 4%, and 6%, respectively. Positive and negative anomalies in columnar water vapor (CWV) and sea surface temperature (SST) across the ITCZ are observed in the wide and narrow regimes, respectively. There is also a strong positive correlation between an El Niño-Southern Oscillation (ENSO) index and ITCZ width anomalies, with wide (narrow) ITCZs occurring during warm (cold) phases of ENSO. This implies that the strengthening and weakening of the Walker circulation associated with ENSO may play a role in modulating the convective populations that contribute to the Pacific ITCZ width variations.

Changes in the frequency and morphology of convection in a warming climate have major implications for the hydrologic cycle and continue to be a large source of variability in climate models. Recent studies of model output indicate a narrowing and intensification of the ascending branch of the Hadley circulation (i.e., the Intertropical Convergence Zone). The present work uses tropical ascent area fraction (Au) and Tropical Rainfall Measurement Mission precipitation features to study global tropical variability in convection with ascent area changes in the current climate. Ascent region convection becomes more intense and organized when Au is low. Overall increases in mean precipitation as the tropical ascent regions shrink are primarily driven by an increase in the areal extent of convective systems, rather than intensity of the convective system rainfall, suggesting an increase in the organization and aggregation of convection as the climate continues to warm.

Until 1966 the parma or white-throated wallaby Macropus parma was believed to have been extinct in Australia for over thirty years. But in that year the authors discovered a considerable number on the New Zealand island of Kawau, where they had been introduced a century ago, as described in Oryx December 1969. Like other wallabies they had been shot and poisoned in considerable numbers because of the damage they do to tree seedlings and agricultural land, but the authors are hopeful that management plans now in hand will ensure their survival unmolested.