The Solar Radiation Climate of Greece

The solar radiation climate of Greece is investigated by using typical meteorological years (TMYs) at 43 locations in Greece based on a period of 10 years (2007–2016). These TMYs include hourly values of global, Hg, and diffuse, Hd, horizontal irradiances from which the direct, Hb, horizontal irradiance is estimated. Use of the diffuse fraction, kd, and the definition of the direct-beam fraction, kb, is made. Solar maps of annual mean Hg, Hd, kd, and kb are prepared over Greece under clear and all skies, which show interesting but explainable patterns. Additionally, the intra-annual and seasonal variabilities of these parameters are presented and regression equations are provided. It is found that Hb has a negative linear relationship with kd; the same applies to Hg with respect to kd or with respect to the latitude of the site. It is shown that kd (kb) can reflect the scattering (absorption) effects of the atmosphere on solar radiation, and, therefore, this parameter can be used as a scattering (absorption) index. An analysis shows that the influence of solar variability (sunspot cycle) on the Hg levels over Athens in the period 1953–2018 was less dominant than the anthropogenic (air-pollution) footprint that caused the global dimming effect.

Global trends in downward surface solar radiation from spatial interpolated ground observations during 1961-2019

Downward surface solar radiation (SSR) is a crucial component of the Global Energy Balance, affecting temperature and the hydrological cycle profoundly, and it provides crucial information about climate change. Many studies have examined SSR trends, however they are often concentrated on specific regions due to limited spatial coverage of ground based observation stations. To overcome this spatial limitation, this study performs a spatial interpolation based on a machine learning method, Random Forest, to interpolate monthly SSR anomalies using a number of climatic variables (various temperature indices, cloud coverage, etc.), time point indicators (years and months of SSR observations), and geographical characteristics of locations (latitudes, longitudes, etc). The predictors that provide the largest explanatory power for interannual variability are diurnal temperature range and cloud coverage. The output of the spatial interpolation is a 0:5° ×0:5° monthly gridded dataset of SSR anomalies with complete land coverage over the period 1961-2019, which is used afterwards in a comprehensive trend analysis for i) each continent separately, and ii) the entire globe.The continental level analysis reveals the major contributors to the global dimming and brightening. In particular, the global dimming before the 1980s is primarily dominated by negative trends in Asia and North America, while Europe and Oceania have been the two largest contributors to the brightening after 1982 and up until 2019.

Homogenized century-long surface incident solar radiation over Japan

Surface incident solar radiation (Rs) plays an essential role in climate change on Earth. Rs can be directly measured, and it shows substantial variability, i.e., global dimming and brightening, on decadal scales. Rs can also be derived from the observed sunshine duration (SunDu) with reliable accuracy. The SunDu-derived Rs was used as a reference to detect and adjust the inhomogeneity in the observed Rs. However, both the observed Rs and SunDu-derived Rs may have inhomogeneity. In Japan, SunDu has been measured since 1890, and Rs has been measured since 1961 at ~100 stations. In this study, the observed Rs and SunDu-derived Rs were first checked for inhomogeneity with a statistical software RHtest. If confirmed by the metadata of these observations, the detected inhomogeneity was adjusted based on the RHtest-quantile matching method. Second, the two homogenized time series were compared to detect further possible inhomogeneity. If confirmed by the independent ground-based observations of cloud cover fraction, the detected inhomogeneity was adjusted based on the reference dataset. As a result, a sharp decrease in the observed Rs from 1961 to 1975 caused by instrument displacement was detected and adjusted. Similarly, a gradual decline in SunDu-derived Rs due to steady instrument replacement from 1985 to 1990 was detected and adjusted. After homogenization, the two estimates agree well. Rs was found to have increased at a rate of 0.9 W m−2 per decade (p < 0.01) from 1961 to 2015 based on the homogenized SunDu-derived Rs, which was enhanced by a positive aerosol-related radiative effect (2.2 W m−2 per decade) and diminished by a negative cloud cover radiative effect (−1.4 W m−2 per decade). The brightening over Japan was the strongest in spring, likely due to a significant decline in aerosol transported from Asian dust storms. The observed raw Rs data and their homogenized time series used in this study are available at https://doi.org/10.11888/Meteoro.tpdc.271524 (Ma et al., 2021).

Relationship Between Sunshine Duration and Air Temperature in Poland (1971–2020)

The aim of the work is to characterize the trends of sunshine duration (SDU) and air temperature, which may help understand the mechanism of contemporary climate change and explain its causes. The daily totals of SDU and daily data on air temperature from the years 1971–2020, from 25 synoptic stations in Poland are the basic source data. There was a growing trend in both SDU and air temperature. The series of records of the two variables showed that the points of change in the level of stabilization of the value of SDU and air temperature are close to each other, and confirm known in the literature “global dimming” and “global brightening” periods. The linear regression model confirmed that sunshine duration explains well the variability of, and increase in day-time air temperature in Poland in the April-September period. In turn, changes in sunshine duration during winter have no impact on air temperature trends.

Diverse trends in observed pan evaporation in South Africa suggest multiple interacting drivers

Planning for future water resource management in a warming climate is confounded when an expectation of increasing evaporation from open water surfaces with global warming is contradicted by observations of secular declines of pan evaporation. Decreasing pan evaporation has been observed globally – a trend which has been attributed variously to declines in wind run (‘global stilling’), declines in radiation (‘global dimming’) and increases in ambient humidity. This contrast between expectation and observation is known as the ‘evaporation paradox’. We evaluated trends in Symons pan evaporation from 154 pans across South Africa. Whilst 59 pans (38% of the 154) showed a statistically significant decrease in observed evaporation rates (p≤0.05), 30 (20%) showed an increase, and 65 (42%) showed no change. These results do not support simple attributions of trends to a common global cause. There is no spatially coherent pattern to trends across South Africa, suggesting that shifts in local drivers of evaporation confound expectations of secular trends due to global drivers. Changes in fetch conditions of the Symons pan installations may be implicated, whereby increasing tree density (through afforestation, alien plant invasion and woody thickening) increases surface friction, reducing wind run, and/or irrigation nearby, increasing local humidity. Correct attribution of the evaporation paradox to reduced wind run in South Africa must consider changing local conditions. Increased tree cover has been observed near a third of the South African Symons pans. Observed evaporation increases for one fifth of pans may implicate expected global drivers for pans where local fetch conditions have remained relatively constant.

The Relationship Between Sunshine Duration And Air Temperature In Poland In The Face Of Contemporary Climate Change

The aim of the work is to characterize the trends of sunshine duration (SDU) and air temperature, which may help understand the mechanism of contemporary climate change and explain its causes. The daily totals of SDU and daily data on air temperature from the years 1971–2019, from 25 synoptic stations in Poland are the basic source data. There was a growing trend in both SDU and air temperature. The series of records of the two variables showed that the points of change in the level of stabilization of the value of SDU and air temperature are close to each other, and confirm known in the literature “global dimming” and “global brightening” periods. The linear regression model confirmed that sunshine duration explains well the variability of, and increase in day-time air temperature in Poland in the April-September period. In turn, changes in sunshine duration during winter have no impact on air temperature trends.

Will COVID-19 Trigger Extinction of All Life on Earth?

The outbreak of the novel coronavirus and the associated COVID-19 is causing an abrupt reduction in industrial activity. As a result of the associated reduction in the aerosol masking effect (“global dimming”), Earth might experience an abrupt rise in global-average temperature. The current temperature of Earth is the highest with Homo sapiens present, suggesting that an abrupt rise in global-average temperature could destroy habitat for humans on Earth. Human extinction could result.