Revisiting the existence of the global warming slowdown during the early 21st century

There are heated debates on the existence of the global warming slowdown during the early 21st century. Although efforts have been made to clarify or reconcile the controversy over the issue, it is not explicitly addressed, restricting the understanding of global temperature change particularly under the background of increasing greenhouse-gas concentrations. Here, using extensive temperature datasets, we comprehensively reexamine the existence of the slowdown under all existing definitions during all decadal-scale periods spanning 1990-2017. Results show that the short-term linear-trend dependent definitions of slowdown make its identification severely suffer from the period selection bias, which largely explains the controversy over its existence. Also, the controversy is further aggravated by the significant impacts of the differences between various datasets on the recent temperature trend and the different baselines for measuring slowdown prescribed by various definitions. However, when the focus is shifted from specific periods to the probability of slowdown events, we find the probability is significantly higher in the 2000s than in the 1990s, regardless of which definition and dataset are adopted. This supports a slowdown during the early 21st century relative to the warming surge in the late 20th century, despite higher greenhouse-gas concentrations. Furthermore, we demonstrate that this decadal-scale slowdown is not incompatible with the centennial-scale anthropogenic warming trend, which has been accelerating since 1850 and never pauses or slows. This work partly reconciles the controversy over the existence of the warming slowdown and the discrepancy between the slowdown and anthropogenic warming.

Decadal trends in climate over India

Decadal variations of meteorological parameters, vig, temperature (surface air maximum temperature, minimum temperature and upper air up to middle troposphere), station level pressure and seasonal and annual rainfall are studied for the period 1901 to 1986 (upper air data available from 1951 onwards), Tests of significance applied to data series (stationwise as well as country as a whole) show that the temperatures are showing a decreasing trend in almost all the northern parts of the country (north of 23" N) and a rising trend in southern parts (south of 23"N), For the country as a whole, however, there is a small warming trend Atmospheric pressure shows a fall between second and third decades but does not indicate any significant change after 1930, Decadal analysis of seasonal (Jun-Sep) and annual rainfall indicates that the variations in rainfall are within the statistical limits.

Microfossil as proxy for palaeoclimate and palaeoceanography

Recent global warming has been addressed due to human activity that causes increased greenhouse gases. However, there are inherent uncertainties in the statement, one of them is the level of natural variability inherent in the climate system. Climate data from measuring instruments are not long enough to evaluate climate variability and current climate evolution. Therefore, we need climate data that has a long back span. To get adequate past climate data, we need natural phenomena which are climate dependent. This natural phenomenon provides a proxy record of the climate. This study of proxy data is the foundation of palaeoclimatology and paleoceanography. Microfossils (i.e., foraminifera, palynomorphs, nannofossils) which in geology are used as a standard tool in biostratigraphy for both age determination and paleoenvironment and correlation, can also be used as a proxy for obtaining paleoclimate and paleoceanography data. Using microfossil as a proxy to study past climate and paleoceanography, we need an understanding of the type of proxy data available and methods used in their analysis.In addition to the dating method (biostratigraphy), there are many climate and oceanography parameters that can be obtained from microfossil proxies such as: sea surface temperature (SST), sea surface salinity, (SST) climate (warm, cold, dry, wet), precipitation, productivity, oxygen content and organic carbon level, deep sea current and ventilation/upwelling, thermocline and mixed layer, variability deep water properties, CCD, bathymetry, sea level change and dissolution. The methods to obtain data fall into some categories e.g., faunal/floral displacement, morphology changes, transfer function/modern analog and isotopic content. Another method that can be used is observing microfossil assemblages and link them to ecological changes associated with climate change and its paleoceanography.A paleoclimate and paleoceanography study using microfossil proxies has been conducted in the Cendrawasih bay, Papua, Indonesia. The study shows that climate in the tropical west Pacific margin (Cendrawasih bay) during Late Pleistocene to Holocene shows high variability. There are nineteen climate changes occurred during Holocene. Early Holocene dated as ca. 11,800-year BP marked by rapid warming with SST differences to last glacial is about 4oC. Early to Middle Holocene (ca. 5960-year BP) marked by increasing temperature up to 2oC, interrupted by cooling at ca. 11230-, 8310- and 7120-years BP. At Middle Holocene temperature decreased rapidly and reached its peak at around ca. 3150-year BP. After cooling at ca. 3150-year BP, temperature increased and then decreased with its peak at ca. 1710-year BP. Since ca. 1710-year BP to Recent, temperature shows warming trend. SST from MAT indicates warming environment near to 1.5oC. The warming trend was interrupted by rapid cooling and warming at ca. 300-year BP. This last warming trend indicates that global warming had started before industrial era and rapid cooling, or warming can occur without anthropogenic gases influence. The typical Holocene climate of warm-wet, dry-cold reverse and become warm-dry, cold-wet during ca. 790-370-year BP and then reversed back to preceding state.Semi-restricted basin occurred since last glacial with anaerobic condition and estuarine circulation system. Warming during interstadial 1e-1a, causing reverse water circulation and basin become sub-aerobic with anti-estuarine circulation. A lot of terrestrial organic matter flow to the bay and increase acidity and carbonate dissolution. High sedimentation found occurred during glacial period especially at the end of glacial period. Rapid warming during late glacial to middle Holocene, rising relative sea level and the bay become more open marine with well oxygenated bottom water and high marine productivity. Warm temperature and deeper thermocline depth (~ 250 m) in west Pacific occurred up to ca. 5960-year BP. Decreasing Sea surface temperature at ca. 5960-year BP and drop of relative sea level causing sub-aerobic condition inside bay. The semi-restricted state with sub-aerobic condition occurred up to Recent.Distribution of Sphaeroidinella group in the tropical west Pacific shows strong correlation with thermocline depth and reflect El Niño frequency event. Early middle Holocene dominated by La Niña-like condition and since Middle Holocene (ca. 5960-year BP) frequent El Niño event began to occur.

Enhanced Warming in Global Dryland Lakes and Its Drivers

Lake surface water temperature (LSWT) is sensitive to climate change. Previous studies have found that LSWT warming is occurring on a global scale and is expected to continue in the future. Recently, new global LSWT data products have been generated using satellite remote sensing, which provides an inimitable opportunity to study the LSWT response to global warming. Based on the satellite observations, we found that the warming rate of global lakes is uneven, with apparent regional differences. Indeed, comparing the LSWT warming in different climate zones (from arid to humid), the lakes in drylands experienced more significant warming (0.28 °C decade−1) than those in semi-humid and humid regions (0.19 °C decade−1) during previous decades (1995–2016). By further quantifying the impact factors, it showed that the LSWT warming is attributed to air temperature (74.4%), evaporation (4.1%), wind (9.9%), cloudiness (4.3%), net shortwave (3.1%), and net longwave (4.0%) over the lake surface. Air temperature is the main driving force for the warming of most global lakes, so the first estimate quantification of future LSWT trends can be determined from air temperature projections. By the end of the 21st century, the summer air temperature would warm up to 1.0 °C (SSP1-2.6) and 6.3 °C (SSP5-8.5) over lakes, with a more significant warming trend over the dryland lakes. Combined with their higher warming sensitivity, the excess summer LSWT warming in drylands is expected to continue, which is of great significance because of their high relevance in these water-limited regions.

Long-Term Spatial and Temporal Variation of Near Surface Air Temperature in Southwest China During 1969–2018

Near surface air temperature (NSAT) is one of the most important climatic parameters and its variability plays a vital role in natural processes associated with climate. Based on an improved ANUSPLIN (short for Australian National University Spline) model which considers more terrain-related factors, this study analyzed the trends, anomalies, change points, and variations of NSAT in Southwest China from 1969 to 2018. The results revealed that the improved approach performed the best in terms of Mean Absolute Error (MAE), Root Mean Square Error (RMSE) and R-squared (R2) comparing to the conventional ANUSPLIN and co-kriging methods. It has great potential for future meteorological and climatological research, especially in mountainous regions with diverse topography. In addition, Southwest China experienced an overall warming trend of 0.21°C/decade for annual mean NSAT in the period 1969–2018. The warming rate was much higher than mainland China and global averages, and statistically significant warming began in the late 1990s. Moreover, consistent warming and significant elevation-dependent warming (EDW) were observed in most parts of Southwest China, and the hiatus or slowdown phenomenon after the 1997/1998 EL Niño event was not observed as expected. Furthermore, the remarkable increase in winter and minimum NSATs contributed more to the whole warming than summer and maximum NSATs. These findings imply that Southwest China responds to global warming more sensitively than generally recognized, and climate change in mountainous regions like Southwest China should be of particular concern.

Trends in surface temperature variability over Mumbai

izs{k.kkRed izek.kksa ls HkweaMy ij lrg rkiekuksa esa m".k izo`fRr dk irk pyrk gSA bl 'kks/k i= esa eqacbZ ds vf/kdre vkSj U;wure rkiekuksa dh izo`fRr;ksa dks Li"V fd;k x;k gSA blesa ,d n’kd ls ysdj izfrnu rd ds fofHkUu dkfyd ekiØeksa ij rkieku izo`fRr;ksa dh tk¡p dh xbZ gSA fo"ke ?kVukvksa ds ?kfVr gksus dh vko`fRr esa izo`fRr;ksa ds fy, ekSle ds leku xq.kksa ds rRoksa dh Hkh tk¡p dh xbZ gSA lkekU;r% eqacbZ esa rkieku dh c<+rh gqbZ izo`fRr ikbZ xbZ gS ftlesa U;wure rkiekuksa dh vis{kk vf/kdre rkieku vf/kd ik;k x;k gS rFkk ;g 95 izfr’kr dh fo’oLrrk Lrj ij lkaf[;dh; :i ls egRoiw.kZ gSA tk¡p dh varj&okf"kZd vkSj varjk ekSle ekuksa nksuksa ij ekWulwu iwoZ vkSj ekWulwu _rqvksa dh vis{kk 'khr _rq vkSj ekWulwuksRrj _rqvksa esa m".krk lfgr ekSleh fHkUurk Li"V :i ls vf/kd ns[kh xbZ gSA pje rkieku ds fo’ys"k.k esa ekSleh fHkUurk Hkh Li"Vr% ns[kh xbZ gSA xeZ fnuksa vkSj xeZ jkrksa esa ?kVukvksa dh vko`fRr 'khr_rq vkSj ekWulwuksRrj _rqvksa dh vis{kk ekWulwu iwoZ vkSj ekWulwu _rqvksa esa vf/kd Li"V :i ls ns[kh xbZ gSA lHkh _rqvksa esa nksuksa LVs’kuksa ij fnu vkSj jkr nksuksa ds le; ds rkiekuksa esa larqfyr m".k izo`fRr ikbZ xbZ gS gk¡ykfd ekWulwuksRrj _rq esa lkarkØqt esa ;g fHkUurk lkaf[;dh; :i ls ux.; ikbZ xbZ gSA Observational evidence points to a warming trend in surface temperatures over the globe. This paper focuses on the trends in Maximum and Minimum temperatures over Mumbai. The temperature trends were investigated at different temporal scales from decadal to daily. The seasonal series were also investigated for trends in frequency of occurrences of extreme events. In general an increasing trend is observed over Mumbai, with the increase in Maximum temperatures more than the Minimum temperatures and statistically significant at 95% confidence level. A seasonal distinction is evident with the warming more in the Winter and Post Monsoon seasons as compared to the Pre Monsoon and Monsoon seasons at both the inter-annual and intra-seasonal scales of investigation. The seasonal distinction was also evident in the extreme temperature analysis. The frequency of occurrences in the hot days and hot nights were more pronounced in the Pre Monsoon and Monsoon seasons as compared to the Winter and Post Monsoon seasons. Symmetric warming trend was observed for both the daytime and nighttime temperatures at both the stations in all the seasons though the variations at Santacruz are statistically insignificant in the Post-Monsoon season

Impact and Variability of Meteorological Parameters on Rice Crop at Siddharthnagar, Uttar Pradesh, India

The present study explores the impacts and variability of meteorological parameter on the rice yields at Siddharthnagar of Uttar Pradesh, India. This study that the maximum and minimum temperatures during the period 2011 to 2020 show increasing trends. Whereas the duration of sunlight increased in June and July. Whereas the rainfall data shows decreasing trends for the period August-September. Furthermore, this study suggests that there was a decrease in rainfall trends during the paddy growing period. A negative correlation was observed with rainfall, particularly during the duff stage, indicating that wetting during the flowering to maturity period may be decisive. This study suggests taking into account the variability of annual or seasonal temperatures and precipitation within the region. The warming trend and irregular precipitation over time may have a significant impact on paddy farming. As a result, plans must be developed to manage the impact of the current variability of meteorological parameters on the paddy yields in this district of Uttar Pradesh by developing appropriate alternatives for increasing paddy crop production.

Weakened Interannual Variability in the Tropical Atlantic

Climate variability in the Tropical Atlantic is complex with strong ocean-atmosphere coupling, where the sea surface temperature (SST) variability impacts the hydroclimate of the surrounding continents. We observe a decrease in the variability of the Tropical Atlantic after 1970 in both CMIP6 models and observations. Most of the Tropical Atlantic interannual variability is explained by its equatorial (Atlantic Zonal Mode, AZM) and meridional (Atlantic Meridional Mode, AMM) modes of variability. The observed wind relaxation after 1970 in both the equatorial and Tropical North Atlantic (TNA) plays a role in the decreased variability. Concerning the AZM, a widespread warming trend is observed in the equatorial Atlantic accompanied by a weakening trend of the trade winds. This drives a weakening in the Bjerknes Feedback by deepening the thermocline in the eastern equatorial Atlantic and increasing the thermal damping. Even though individually the TNA and Tropical South Atlantic (TSA) show increased variability, the observed asymmetric warming in the Tropical Atlantic and relaxed northeast trade winds after the 70s play a role in decreasing the AMM variability. This configuration leads to positive Wind-Evaporation-SST (WES) feedback, increasing further the TNA SST, preventing AMM from changing phases as before 1970. Associated with it, the African Sahel shows a positive precipitation trend and the Intertropical Convergence Zone tends to shift northward, which acts on maintaining the increased precipitation.

Variability and time series trend analysis of temperature over 1981-2018 in semi-arid Borana zone, southern Ethiopia

BackgroundUnderstanding the climate variability at local scale could help suggest local adaptation responses to manage climate driven impacts. This paper analyzed the variability and trends of temperature over the period 1981-2018 in semi-arid Borana zone of southern Ethiopia using Mann-Kendall (MK) test and inverse distance weighted (IDW) interpolation technique. Gridded (4 km * 4 km) daily temperature data was used to study variability at temporal and spatial scales. ResultsThe results revealed that monthly temperature shows a warming trend where February was the warmest month for both maximum and minimum temperature. Seasonally, the highest maximum and minimum temperatures were observed during Bega. Minimum temperature shows a warming trend during all seasons unlike maximum temperature. Both minimum and maximum temperature shows not significant warming trend at annual timescale. The later decades (20012018) have shown a warming trend compared to a period ahead especially for minimum temperature. The southwestern and southeastern areas across the zone were warmer than any other areas in the region during the studied period. ConclusionTemperature shows variability at shorter than longer timescales. There is a pronounced warming trend for minimum than maximum temperature. Warming condition advances from the northcentral parts towards the southwestern and southeastern areas. Internal variability was observed at temporal and spatial scales and therefore any adaptation responses to local climate variability should consider the microscale climate.