Assessing anthropogenic climate change in a regional context is challenging due to the spatial heterogeneity of climatic variables and is more complicated than at the global scale. Especially in the Tropics, such spatial variations are expected to increase, warranting the identification of homogeneous climatic zones for assessing regional climate change. The present study explores the ability of bioclimatic variables in defining regional climatic zones, and the detection of climate change therein. We hypothesize that the identification of homogeneous climatic zones based on bioclimatic variables could be an effective approach rather than the conventional extreme climate-based indices to identify climate change signals. To demonstrate the hypothesis, bioclimatic variables representing the generalized climatic characteristics of a tropical river basin were derived from observed gridded datasets of rainfall and temperature. Clusters of homogeneous climatic zones were identified, and their temporal variations were analysed to examine the existence of climate change. The results indicate that despite the spatial heterogeneity in extreme climate-based indices, the bioclimatic variables-based approach renders a meaningful representation of the regional climatic pattern. Investigation of bioclimatic zones of the study area helped to identify a shift in its climatic zones with a slant towards drier conditions. Further, future changes in climatic zones were identified from 13 different GCMs that participated in the CMIP6, projecting drier conditions over the basin, with varying spatial extend based on future emission scenarios. The study significantly contributes towards the identification of climatologically fragile regions in changing climate, which is an essential component in developing any regional climate change adaptation and mitigation strategy.

The 2023 Antarctic sea ice extent (SIE) maximum on 7 September was the lowest annual maximum in the satellite era (16.98 × 10⁶ km²), with the largest contributions to the anomaly coming from the Ross (37.7%, −0.57 × 10⁶ km²) and Weddell (32.9%, −0.49 × 10⁶ km²) Seas. The SIE was low due to anomalously warm (>0.3°C) upper-ocean temperatures combined with anomalously strong northerly winds impeding the ice advance during the fall and winter. Northerly winds of >12 ms⁻¹ in the Weddell Sea occurred because of negative pressure anomalies over the Antarctic Peninsula, while those in the Ross Sea were associated with extreme blocking episodes off the Ross Ice Shelf. The Ross Sea experienced an unprecedented SIE decrease of −1.08 × 10³ km² d⁻¹ from 1 June till the annual maximum. The passage of quasi-stationary and explosive polar cyclones contributed to periods of southward ice-edge shift in both sectors.

We investigate an unusual extensive ice-free feature (EIF) within the pack ice that developed in the central Weddell Sea in December 1980 on the edge of the multi-year sea ice off the east coast of the Antarctic Peninsula. The EIF was first apparent on satellite imagery on 8 December 1980 and expanded until it reached its largest areal extent of ~5.4 × 10⁵km² on 26 December. The combined influences of near-record strength ( ~ 15 ms⁻¹) cold winds from the Antarctic continent (transporting sea ice northward and creating an area of thin ice), increased shortwave radiation and net heat flux into the ocean, passage of deep polar storms, and the upwelling of high saline warm water led to the opening of this unique EIF. It is still the largest ice-free feature within the pack ice resembling a polynya observed in the central Weddell Sea during the satellite era, contributing significantly to the 1981 Weddell Sea sea ice extent minimum of 0.793 × 10⁶km², the lowest on record. The development mechanism of this EIF was different from the 1970’s Weddell open ocean polynya which occurred within the winter sea ice cover through enhanced ocean convection.

The optical characteristics of colored dissolved organic matter (CDOM) serve as a convenient tool for evaluating coastal processes, e.g., river runoff, anthropogenic inputs, primary production, and bacterial/photochemical processes. We conducted a study on the seasonal and spatial variability of absorbance and fluorescence characteristics of CDOM and nutrients in the coastal waters near the Gauthami estuary of River Godavari, the largest peninsular river of India, for a year. The surface aCDOM(350) showed a significant inverse relation with salinity in the coastal region, indicating a conservative mixing of marine and terrestrial end members. The aCDOM(350) was not conservative in the offshore (100 m isobath) waters due to enrichment by secondary sources. Seasonal variability in optical properties indicated diverse sources for CDOM, as revealed by principal component analysis. The excitation-emission matrix (EEM) spectra followed by parallel factor analysis (EEM-PARAFAC) revealed four distinct fluorophores. The tyrosine (B) fluorophore showed a predominant increase in the post-monsoon season (October to January), while tryptophan (T) was relatively more enriched, coincident with nutrient enrichment and transparency increase during the early monsoon phase (July). The biological index (BIX), which reflects recent photosynthetic activity, also displayed relatively higher values during the early monsoon. The humic fluorophores A and M, and humification index (HIX) were relatively enriched during the later phase of monsoon (July–October). HIX was > 4 in a few samples of the offshore region (100-m isobath) and indicated a probable contamination from drill-mud (bentonite) used in hydrocarbon exploration. During the monsoon, the relationship between T and B with CDOM was not evident due to the masking of B fluorescence in intact protein. However, during the post-monsoon (POM) and pre-monsoon (PRM) periods, this masking effect was not observed, likely due to protein degradation via bacterial and photochemical processes, respectively. Temporal variability in nutrients indicated that high ammonium levels were produced during POM (OM bacterial degradation), and high nitrite levels were observed during PRM (due to primary production). This study provides foundational insights into the use of CDOM for understanding the impact of diverse environmental, river discharge, and anthropogenic factors on coastal ecosystems.

The present climate change phase has had contrasting effects on sea ice in the Arctic and Antarctic. There has been a startling loss of ancient ice in the Arctic, leading to a dramatic reduction in sea-ice area and thickness. No evidence of analogous shifts in the Antarctic has been found till 2014. This work seeks to understand the issue presented in the title by synthesizing relevant research from the literature. This chapter begins by reviewing important recent records and defining major geographical and meteorological aspects and sea-ice characteristics of the two polar areas. More specifically satellite data revealed that the Antarctic sea-ice extent is increasing at a rate of 0.7 ± 0.4 percent decade−1 (1979–2018). On the contrary, the Arctic sea ice showed a decreasing trend as an optimal consequence of global warming at a rate of −4.8 ± 0.2 percent decade−1 (1979–2018). This study explored 40 years (1979–2018) of Antarctic sea-ice remote sensing data to explore its overall and regional trends. Anomaly has been computed over the previous 3 years (2015, 2016, 2017, and 2018) to determine what form of anomaly has arisen in the Antarctic area. The findings of this study have the potential to understand the drivers and dynamics of Antarctic sea ice and contribute to future climate projections.