A global inventory of historical documentary evidence related to climate since the 15th century

Climatic variations have impacted societies since the very beginning of human history. In order to keep track of climatic changes over time, humans have thus often closely monitored the weather as well as natural phenomena influencing everyday life. Resulting documentary evidence from archives of societies enables invaluable insights into the past climate beyond the timescale of instrumental and early instrumental measurements. This information complements other proxies from archives of nature such as tree rings in climate reconstructions, as documentary evidence often covers seasons (e.g., winter) and regions (e.g., Africa, Western Russia, and Siberia, China) that are not well covered with natural proxies. While a mature body of research on detecting climate signals from historical documents exists, the large majority of studies is confined to a local or regional scale and thus lacks a global perspective. Moreover, many studies from before the 1980s have not made the transition into the digital age and, hence, are essentially forgotten. Here, I attempt to compile the first-ever systematic global inventory of documentary evidence related to climate extending back to the Late Medieval Period. It combines information on past climate from all around the world, retrieved from many studies on historical documentary sources. Historical evidence range from personal diaries, chronicles, administrative/ clerical documents to ship logbooks and newspaper articles. They include records of many sorts, e.g., tithes records, rogation ceremonies, extreme events like droughts and floods, as well as weather and phenological observations. The inventory, published as an electronic supplement, comprises detailed event chronologies, time series, proxy indices, and calibrated reconstructions, with the majority of the documentary records providing indications on past temperature and precipitation anomalies. The overall focus is on document-based time series with significant potential for climate reconstruction. For each included record series, extensive meta information and directions to the data (if available) are given. To highlight the potential of documentary data for climate science three case studies are presented and evaluated with different global reanalysis products. This comprehensive inventory promotes the first-ever global perspective on historical documentary climate records and, thus, lies the foundation for incorporating historical documentary evidence into climate reconstruction on a global scale, complementing early instrumental measurements as well as natural climate proxies.

Modelling Methane Hydrate Saturation in Pores: Capillary Inhibition Effects

Experimental and field observations evidence the effects of capillarity in narrow pores on inhibiting the thermodynamic stability of gas hydrates and controlling their saturation. Thus, precise estimates of the gas hydrate global inventory require models that accurately describe gas hydrate stability in sediments. Here, an equilibrium model for hydrate formation in sediments that accounts for capillary inhibition effects is developed and validated against experimental data. Analogous to water freezing in pores, the model assumes that hydrate formation is controlled by the sediment pore size distribution and the balance of capillary forces at the hydrate–liquid interface. To build the formulation, we first derive the Clausius–Clapeyron equation for the thermodynamic equilibrium of methane and water chemical potentials. Then, this equation is combined with the van Genuchten’s capillary pressure to relate the thermodynamic properties of the system to the sediment pore size distribution and hydrate saturation. The model examines the influence of the sediment pore size distribution on hydrate saturation through the simulation of hydrate formation in sand, silt, and clays, under equilibrium conditions and without mass transfer limitations. The results show that at pressure–temperature conditions typically found in the seabed, capillary effects in very fine-grained clays can limit the maximum hydrate saturation below 20% of the host sediment porosity.

Accounting for all territorial emissions and sinks is important for development of climate mitigation policies

The Paris agreement identifies the importance of the conservation, or better, increase of the land carbon sink. In this respect, the mitigation policies of many forest rich countries rely heavily on products from forests as well as on the land sink. Here we demonstrate that Sweden’s land sink, which is critical in order to achieve zero net emissions by 2045 and negative emissions thereafter, is reduced to less than half when accounting for emissions from wetlands, lakes and running waters. This should have implications for the development of Sweden’s mitigation policy. National as well as the emerging global inventory of sources and sinks need to consider the entire territory to allow accurate guidance of future mitigation of climate change.

Visible, potential, and functional land degradation assessment in southern Africa

Land degradation in drylands threatens vulnerable ecosystems and socioeconomic development. Currently, NDVI derived from remotely sensed data is the main tool used for degradation detection. Three indicators have usually been used to detect land degradation: (1) NDVI trends for visible degradation, (2) residual for human-induced potential degradation, and (3) sensitivity of vegetation to rainfall for functional degradation. However, few studies have integrated and compared these three indicators. In this study, we used Global Inventory Monitoring and Modelling System Version (GIMMS 3.1) NDVI dataset and Multiple Source Weighted-Ensemble Precipitation (MSWEP) rainfall dataset (1982-2015) and applied linear regression, Time Series Segmented and Residual Trend (TSS-RESTREND), and Sequential Regression (SeRGs) methods to detect degradation in southern Africa. The results showed that degradation was detected by these three respective indicators in 18.7%, 11.3%, and 7.1% of the study area. Degradation from any one type was found to occupy 27.21% of the total area, whereas the co-occurrence of two or more types only occupied 3.84%. These results indicate the dominant discrepancies among these indicators and the independent relationships among the degradation processes. Despite significantly greening, potential degradation and functional degradation were still observed. On the regional scale, spatial patterns of degradation were affected by different levels of aridity. On the national scale, the proportions of degradation were still influenced by increased population, inadequate policies, and other factors. This study highlights the need to detect degradation with multiple indicators and improves our understanding of degradation types and intensity.

A global inventory of potential future glacial lakes

<p>A prominent phenomenon accompanying glacier retreat is the formation of new lakes. Such glacial lakes are the subject of numerous studies and investigations due to their potential to produce far-reaching glacial lake outburst floods (GLOFs), but also because they might provide opportunities for water resource management and energy production. Here we present a first global inventory of potential future glacial lakes, along with expected formation times under different RCP scenarios.</p><p>From published datasets of ice thickness distributions of all glaciers of the world, we identified glacier bed overdeepenings and extracted parameters of potential future lakes, such as area, depth and volume. The consideration of the ensemble of ice thicknesses allowed for a first-order quantification of uncertainties. We identified 67,000 (ranging from 55,000 to 87,000) overdeepenings with volumes larger than 1 x 10<sup>6</sup> m<sup>3</sup>, the total surface area and volume of corresponding potential lakes is 61,000 (56,000 to 64,000) km<sup>2</sup> and 4,600 (3,100 to 7,200) km<sup>3</sup>, respectively. However, these numbers are based on the assumption of fully water-filled overdeepenings and therefore represent upper bound estimates. Global results are strongly influenced by very large depressions identified beneath (flat) polar glaciers and ice caps.  We then combined potential future lake sites with estimated future glacier extents from a global glacier evolution model (GloGEM), in order to estimate formation periods of these future lakes, considering different RCPs. Strong regional differences are also found in the anticipated formation periods: While in the low latitudes most future lakes are expected to form in the current decade, irrespective of the RCP, Arctic regions have highest lake formation rates towards the end of the 21<sup>st</sup> century, with the majority of bed overdeepening not being exposed by glacier retreat until 2100. In mid latitude mountain regions, large differences between RCP2.6 and RCP8.5 exist in regard of the timing of lake formation and the amount of total uncovered overdeepenings.</p><p>In addition to geometric properties and expected formation periods, the topographic potential for impacting mass movements, such as rock or ice avalanches, is determined for each overdeepening. In combination with potential lake volume and watershed area of the lake, these characteristics can be used for a first order estimation of lake outburst susceptibility. With a basic flow routing algorithm, potential outburst trajectories are modeled for each overdeepening. In combination with information on population density, settlements and further socio-economic and environmental datasets, this information can be used for future analyses of hazards, risks and opportunities associated with these potential future glacial lakes.</p>