Identifying human influences on atmospheric temperature

Remote Sensing, 2016

This review paper discusses how to develop, produce, sustain, and serve satellite climate data records (CDRs) in the context of transitioning research to operation (R2O). Requirements and critical procedures of producing various CDRs, including Fundamental CDRs (FCDRs), Thematic CDRs (TCDRs), Interim CDRs (ICDRs), and climate information records (CIRs) are discussed in detail, including radiance/reflectance and the essential climate variables (ECVs) of land, ocean, and atmosphere. Major international CDR initiatives, programs, and projects are summarized. Societal benefits of CDRs in various user sectors, including Agriculture, Forestry, Fisheries, Energy, Heath, Water, Transportation, and Tourism are also briefly discussed. The challenges and opportunities for CDR development, production and service are also addressed. It is essential to maintain credible CDR products by allowing free access to products and keeping the production process transparent by making source code and documentation available with the dataset.

Nature

Although anthropogenic climate change is expected to have caused large shifts in temperature and rainfall, the detection of human influence on global drought has been complicated by large internal variability and the brevity of observational records. Here we address these challenges using reconstructions of the Palmer drought severity index obtained with data from tree rings that span the past millennium. We show that three distinct periods are identifiable in climate models, observations and reconstructions during the twentieth century. In recent decades (1981 to present), the signal of greenhouse gas forcing is present but not yet detectable at high confidence. Observations and reconstructions differ significantly from an expected pattern of greenhouse gas forcing around mid-century (1950-1975), coinciding with a global increase in aerosol forcing. In the first half of the century (1900-1949), however, a signal of greenhouse-gas-forced change is robustly detectable. Multiple observational datasets and reconstructions using data from tree rings confirm that human activities were probably affecting the worldwide risk of droughts as early as the beginning of the twentieth century.

Scientific Reports

The terrestrial phase of the water cycle can be seriously impacted by water management and human water use behavior (e.g., reservoir operation, and irrigation withdrawals). Here we outline a method for assessing water availability in a changing climate, while explicitly considering anthropogenic water demand scenarios and water supply infrastructure designed to cope with climatic extremes. The framework brings a top-down and bottom-up approach to provide localized water assessment based on local water supply infrastructure and projected water demands. When our framework is applied to southeastern Australia we find that, for some combinations of climatic change and water demand, the region could experience water stress similar or worse than the epic Millennium Drought. We show considering only the influence of future climate on water supply, and neglecting future changes in water demand and water storage augmentation might lead to opposing perspectives on future water availability. While human water use can significantly exacerbate climate change impacts on water availability, if managed well, it allows societies to react and adapt to a changing climate. The methodology we present offers a unique avenue for linking climatic and hydrologic processes to water resource supply and demand management and other human interactions. Water resources are sensitive to climate change and variability 1-5 , especially in arid and semi-arid regions 6-8. Regional and global hydrologic models forced with Global climate model simulations have been widely used to assess future changes in water resources 9-11. Water availability is also closely associated with operations of water supply infrastructure (surface water reservoirs and desalination plants, etc.), and human water use behavior (e.g., growth and seasonal cycles in water demands) 12. Some modeling frameworks used for climate/hydrology projections typically simulate the natural hydrologic cycle 13-17 (Fig. 1 (top right)) without considering anthropogenic water demand, human interactions 18, 19 and man-made infrastructure such as dams and reservoirs 20 (Fig. 1(top left)). Storage infrastructure can significantly alter water flow and distribution 21. Man-made surface reservoirs control 22 about 20% of the global annual river discharge (~8000 km 3 out of 40000 km 3 ; ref. 23) and provide resilience against droughts, in addition to their role in water resource management and energy production 24-27. Since early 2000s, several major modeling efforts have tackled integrating water demand, irrigation and other human dimensions in water stress and availability analysis 10, 28-41. Man-made local water supply infrastructure (in particular surface water reservoirs) affects future water availability because it is, generally speaking, built specifically to cope with climatic extremes. A system with distributed and different water storage, and therefore more local resilience, will be less vulnerable to climatic change and variability compared to a system with limited local capacity to cope with extremes. As a result, different regions will see different water availability changes depending on their local infrastructure and capacity to cope with variability or adapt to change. Omitting surface water reservoirs from large-scale water cycle models introduces a large source of uncertainty in current assessments of the global water cycle and hinders evaluation of climate change

Scientific Reports, 2017

Surface Temperature (ST) over India has increased by ~0.055 K/decade during 1860-2005 and follows the global warming trend. Here, the natural and external forcings (e.g., natural and anthropogenic) responsible for ST variability are studied from Coupled Model Inter-comparison phase 5 (CMIP5) models during the 20 th century and projections during the 21 st century along with seasonal variability. Greenhouse Gases (GHG) and Land Use (LU) are the major factors that gave rise to warming during the 20 th century. Anthropogenic Aerosols (AA) have slowed down the warming rate. The CMIP5 projection over India shows a sharp increase in ST under Representative Concentration Pathways (RCP) 8.5 where it reaches a maximum of 5 K by the end of the 21 st century. Under RCP2.6 emission scenarios, ST increases up to the year 2050 and decreases afterwards. The seasonal variability of ST during the 21 st century shows significant increase during summer. Analysis of rare heat and cold events for 2080-2099 relative to a base period of 1986-2006 under RCP8.5 scenarios reveals that both are likely to increase substantially. However, by controlling the regional AA and LU change in India, a reduction in further warming over India region might be achieved.

Remote Sensing, 2015

The tropospheric and stratospheric temperature trends and uncertainties in the fifth Coupled Model Intercomparison Project (CMIP5) model simulations in the period of 1979-2005 have been compared with satellite observations. The satellite data include those from the Stratospheric Sounding Units (SSU), Microwave Sounding Units (MSU), and the Advanced Microwave Sounding Unit-A (AMSU). The results show that the CMIP5 model simulations reproduced the common stratospheric cooling (´0.46-´0.95 K/decade) and tropospheric warming (0.05-0.19 K/decade) features although a significant discrepancy was found among the individual models being selected. The changes of global mean temperature in CMIP5 simulations are highly consistent with the SSU measurements in the stratosphere, and the temporal correlation coefficients between observation and model simulations vary from 0.6-0.99 at the 99% confidence level. At the same time, the spread of temperature mean in CMIP5 simulations increased from stratosphere to troposphere. Multiple linear regression analysis indicates that the temperature variability in the stratosphere is dominated by radioactive gases, volcanic events and solar forcing. Generally, the high-top models show better agreement with observations than the low-top model, especially in the lower stratosphere. The CMIP5 simulations underestimated the stratospheric cooling in the tropics and overestimated the cooling over the Antarctic compared to the satellite observations. The largest spread of temperature trends in CMIP5 simulations is seen in both the Arctic and Antarctic areas, especially in the stratospheric Antarctic.

Environment Systems and Decisions, 2014

The science is clear that climate change is one of the most important issues facing humanity. The changing climate is already affecting humanity and our economies in many ways. These effects will increase as the climate continues to change, and the effects are expected to increase dramatically over the coming decades. Climaterelated hazards exacerbate other stressors, often with negative outcomes for livelihoods, especially for people living in poverty. Climate change can amplify existing stresses and vulnerabilities among populations and existing threats to security and can indirectly increase risks of violence and violent conflict. This paper is aimed at examining the changes occurring to the Earth's climate, what additional changes in climate are likely to occur over the coming decades, and how climate change could affect global security.

Scientific reports, 2017

Satellite temperature measurements do not support the recent claim of a "leveling off of warming" over the past two decades. Tropospheric warming trends over recent 20-year periods are always significantly larger (at the 10% level or better) than model estimates of 20-year trends arising from natural internal variability. Over the full 38-year period of the satellite record, the separation between observed warming and internal variability estimates is even clearer. In two out of three recent satellite datasets, the tropospheric warming from 1979 to 2016 is unprecedented relative to internally generated temperature trends on the 38-year timescale.

Nature Geoscience, 2017