Firn Evolution at Camp Century, Greenland: 1966–2100

Camp Century is an American military base built in 1959 under the surface of the Greenland ice sheet and decommissioned in 1967. Here, we use outputs from RACMO2.3p2 and CanESM2 climate models, adjusted to meteorological observations, and a firn model to simulate the firn density and temperature at Camp Century between 1966 and 2100. The model output is evaluated against an extensive set of firn 3observations and three Representative Concentration Pathways (RCP2.6, 4.5 and 8.5) are considered as future scenarios. Our model suggests that the upper horizon of the Camp Century debris field – observed at a depth of 32 m in 2017 – will continue to be buried by persistent net accumulation over the next eighty years under all RCP scenarios. This horizon depth will be between 58 and 64 m in 2100, depending on the RCP scenario. We estimate a maximum meltwater percolation depth of 1.1 m under all RCP scenarios. We therefore find it extremely unlikely that surface meltwater interacts with the subsurface debris field at Camp Century before 2100 under all RCP scenarios. Camp Century’s future is representative of the firn area in northwestern Greenland, bound to shift from dry snow to a percolation regime. Our model suggests that 10 m firn temperatures at Camp Century will increase from −24.0°C in 1966 to −21.3, −20.0 and −18.6°C in 2100 under the RCP2.6, 4.5 and 8.5 scenarios, respectively. We reveal a previously unknown warm bias in air temperatures simulated at Camp Century by both RACMO2.3p2 and CanESM2 climate models which needs to be accounted for when using these models to predict melt, firn evolution and sea-level contribution of the Greenland ice sheet. We also present novel in situ measurements of firn compaction rates, which indicate that about 25% of firn compaction of the top 62 m of firn occurs below 20 m depth. This highlights the importance of deep-firn compaction measurements for model evaluation and correction of altimetry products.

Timing of rates and magnitude of sea-level rise projection families

<p>In the past decade, many different projections of global and regional sea-level rise as a result of climate change have been published (Garner et al, 2018, Horton et al, 2018). This wide range of projections illustrates the large uncertainty about future sea-level rise, which is complicated for coastal decision makers relying on these projections. Here, we aim to provide insights into the available projections, by identifying the main contributing sources in each of the sea-level projections, and sorting the projections into ‘families’ that have contributing sources or methodologies in common. Using these ‘families’, we discuss the main differences between projections in terms of rates and timing of certain levels of sea-level rise. </p><p>Sea-level rise projections are often compared by showing amounts or rates at a certain future point in time, e.g., 2050 or 2100. For many areas, a sea-level rise exceeding 1 to 2 m will require truly transformative decisions. Such decisions have a long lead time (in the order of 30 years) for planning and implementation. Showing the timing of a particular rate or magnitude of sea-level rise may provide insight that it is not a matter of if and how to adapt, but when to adapt. This may help decision makers in dealing with the uncertainties and it may accelerate adaptation.</p><p>We find that a sea-level rise of 25 cm (since 2000) is first reached for each of the RCP scenarios (the 95<sup>th</sup> percentile) within a decade of each other. This indicates that for a structure with a lifetime based on a sea-level rise of 25 cm, decisions are not conditional on the RCP scenario. The latest year for crossing the 25 cm threshold (the 5<sup>th</sup> percentile), however, does depend more on the RCP scenario: for the RCP2.6 scenario this is later than for the RCP8.5 scenario, because the acceleration is less strong. As the levels examined grow (0.25 m, 0.5 m, 0.75 m, etc.), the initial year of reaching that level starts to diverge more between the scenarios, and therefore the timing of decision points starts to be more and more conditional upon RCP scenario. However, for investments with a long envisioned lifetime such as coastal infrastructure, certain amounts of sea level rise may still be within the lifetime independent of the RCP scenario.</p><p> </p>

Uncertainty sources in simulated ecosystem indicators of the 21st century climate change

The forest ecosystems are already responding to increased CO2 concentrations and changing environmental conditions. These ongoing developments affect how societies can utilise and benefit from the woodland areas in the future, be it e.g. climate change mitigation as carbon sinks, lumber for wood industry or preserved for nature tourism and recreational activities. We assess the effect and the relative magnitude of different uncertainty sources in ecosystem model simulations from the year 1980 to 2100 for two Finnish boreal forest sites. The models used in this study are the land ecosystem model JSBACH and the forest growth model PREBAS. The considered uncertainty sources for both models are model parameters, four prescribed climates and two RCP (Representative Concentration Pathway) scenarios. PREBAS simulations also include an additional RCP scenario and two forest management actions. We assess the effect of these sources at four different stages of the simulations on several ecosystem indicators of climate change, e.g. gross primary production (GPP), ecosystem respiration, soil moisture, recurrence of drought, length of the vegetation active period (VAP), length of the snow melting period and the stand volume. The climate model uncertainty remains roughly the same throughout the simulations and is overtaken by the RCP scenario impact halfway through the experiment. The management actions are the most dominant uncertainty factors for Hyytiälä and as important as RCP scenarios at the end of the simulations, but contribute only half as much for Sodankylä. The parameter uncertainty is the most elusive to estimate due to non-linear and adverse effects on the simulated ecosystem indicators.

Worldwide soil moisture changes driven by future hydro-climatic change scenarios

Soil moisture is a key variable in hydrology, ecology, and climate change science. It is also of primary importance for the agricultural and water resource sectors of society. This paper investigates how hydro-climatic changes, projected by 14 CMIP5 models and for different radiative forcing (RCP) scenarios to occur from 2006-2025 to 2080-2099, may affect different soil moisture aspects in 81 large catchments worldwide. Overall, for investigated changes in dry/wet event occurrence and in average value and inter-annual variability of seasonal water content, different RCP scenarios imply opposite directions of change in around half or more of the study catchments. Regardless of RCP scenario, the greatest projected changes are found for the inter-annual variability of seasonal soil water content. Especially for the dry-season water content, large increases in inter-annual variability emerge for several large catchments over the world; the considered RCP scenario determines precisely which these catchments are.