Global-scale surface salinity change since the 1870s.Implications for the global hydrological cycle

<p>Based on the first ever combined analysis of observations from the round-the-world voyages of HMS Challenger and SMS Gazelle in the 1870s, early in the industrial era, this paper shows that the amplification of the global surface salinity signal (saline areas becoming saltier and fresh areas fresher) has increased by 63±5% since the 1950s compared to the period 1870s to 1950s. Other analyses of regional salinity change between the mid-20<sup>th</sup> century and present day have linked this amplification to anthropogenically-driven strengthening of the global hydrological cycle in line with increasing global temperatures. Our results show that the rate of change has indeed accelerated but more closely in line with changes in sea surface temperature than with surface air temperature over almost 150 years. This is the first global-scale analysis of salinities from these two expeditions in the 1870s and the first observational evidence of changes in the global hydrological cycle since the late 19<sup>th</sup> century.</p>

Revisiting the global hydrological cycle: is it intensifying?

As a result of technological advances in monitoring atmosphere, hydrosphere, cryosphere and biosphere, as well as in data management and processing, several databases have become freely available. These can be exploited in revisiting the global hydrological cycle with the aim, on the one hand, to better quantify it and, on the other hand, to test the established climatological hypotheses according to which the hydrological cycle should be intensifying because of global warming. By processing the information from gridded ground observations, satellite data and reanalyses, it turns out that the established hypotheses are not confirmed. Instead of monotonic trends, there appear fluctuations from intensification to deintensification, and vice versa, with deintensification prevailing in the 21st century. The water balance on land and in the sea appears to be lower than the standard figures of literature, but with greater variability on climatic timescales, which is in accordance with Hurst–Kolmogorov stochastic dynamics. The most obvious anthropogenic signal in the hydrological cycle appears to be the over-exploitation of groundwater, which has a visible effect on the rise in sea level. Melting of glaciers has an equal effect, but in this case it is not known which part is anthropogenic, as studies on polar regions attribute mass loss mostly to ice dynamics.

Revisiting global hydrological cycle: Is it intensifying?

As a result of technological advances in monitoring atmosphere, hydrosphere, cryosphere and biosphere, as well as in data management and processing, several data bases have become freely available. These can be exploited in revisiting the global hydrological cycle with the aim, on the one hand, to better quantify it and, on the other hand, to test the established climatological hypotheses, according to which the hydrological cycle should be intensifying because of global warming. By processing the information from gridded ground observations, satellite data and reanalyses, it turns out that the established hypotheses are not confirmed. Instead of monotonic trends, there appear fluctuations from intensification to deintensification and vice versa, with deintensification prevailing in the 21st century. The water balance on land and sea appears to be lower than the standard figures of literature, but with greater variability on climatic time scales, which is in accordance with Hurst-Kolmogorov stochastic dynamics. The most obvious anthropogenic signal in the hydrological cycle appears to be the overexploitation of groundwater, which has a visible effect on sea level rise. Melting of glaciers has an equal effect, but in this case it in not known which part is anthropogenic, as studies on polar regions attribute mass loss mostly to ice dynamics.