Low-pressure systems of type Vb may trigger heavy rainfall events over central Europe. This study aims at analysing the relative role of their moisture sources. For this, a set of sensitivity experiments encompassing changes in soil moisture and Atlantic Ocean and Mediterranean Sea SSTs are carried out with WRF. The latter moisture source stands out as the most relevant one. Furthermore, the regions most affected by Vb events in the future might be shifted from the Alps to the Balkan Peninsula.
Monsoon systems have undergone abrupt changes in past climates, and theoretical considerations show that threshold behavior can follow from the internal dynamics of monsoons. So far, however, the possibility of abrupt changes has not been explored for modern monsoon systems. We analyze state-of-the-art climate model simulations and show that some models project abrupt changes in Sahel rainfall in response to a dynamic shift in the West African monsoon under 21st century climate change.
Dynamical downscaling of climate fields at very high resolutions (convection- and topography-resolving scales) over the complex Himalayan terrain of the Nepalese Himalayas shows promising results. It clearly demonstrates the potential of mesoscale models to accurately simulate present and future climate information at very high resolutions over remote, data-scarce mountainous regions for the development of adaptation strategies and impact assessments in the context of changing climate.
The rapidly growing forest-based bioeconomy calls for increasing wood harvesting intensity, and an increase in thinning and a final felling area. This may increase wind damage risks at the upwind edges of new cleared felling areas and thinned stands. Efficient wind risk assessment is needed. We demonstrate a pragmatic and computationally feasible method for identifying at a high spatial resolution those locations having the highest forest wind damage risks.
In lowland Bolivia, satellite images show rivers collapsing and the replacement of forest with savannah. This was first described in 1996 as the result of logjams (river dams created by fallen trees). I have investigated how the logjams form and affect the forest through remote sensing and fieldwork. Logjams occur nearly every year and propagate upriver until the river changes course. This region offers a unique opportunity to study how frequent forest die-off events affect biodiversity.
James Hansen, Makiko Sato, Pushker Kharecha, Karina von Schuckmann, David J. Beerling, Junji Cao, Shaun Marcott, Valerie Masson-Delmotte, Michael J. Prather, Eelco J. Rohling, Jeremy Shakun, Pete Smith, Andrew Lacis, Gary Russell, and Reto Ruedy
Global temperature now exceeds +1.25 °C relative to 1880–1920, similar to warmth of the Eemian period. Keeping warming less than 1.5 °C or CO2 below 350 ppm now requires extraction of CO2 from the air. If rapid phaseout of fossil fuel emissions begins soon, most extraction can be via improved agricultural and forestry practices. In contrast, continued high emissions places a burden on young people of massive technological CO2 extraction with large risks, high costs and uncertain feasibility.
Recent UNFCCC climate meetings have placed much emphasis on constraining global warming to remain below 2 °C. The 2015 Paris meeting went further and gave an aspiration to fulfil a 1.5 °C threshold. We provide a flexible set of algebraic global temperature profiles that stabilise to either target. This will potentially allow the climate research community to estimate local climatic implications for these temperature profiles, along with emissions trajectories to fulfil them.
Drought effect on vegetation in the eastern part of the Baltic Sea region was determined using satellite data. The impact of precipitation deficit on vegetation on arable land and in broadleaved and coniferous forests was analysed. The precipitation deficit in the first part of the growing season only has a significant impact on the vegetation on arable land, while this impact becomes more evident in all types of vegetation in the second half of the season.
We statistically analyse the relationship between the structure of migrating dunes in the southern Baltic and the driving wind conditions over the past 26 years, with the long-term aim of using migrating dunes as a proxy for past wind conditions at an interannual resolution.
Anomalies and extremes are often detected using univariate peak-over-threshold approaches in the geoscience community. The Earth system is highly multivariate. We compare eight multivariate anomaly detection algorithms and combinations of data preprocessing. We identify three anomaly detection algorithms that outperform univariate extreme event detection approaches. The workflows have the potential to reveal novelties in data. Remarks on their application to real Earth observations are provided.
We discuss for the first time changes in the wave climate in the Baltic Sea over the last 2 decades derived from satellite altimetry data spanning over 26 years. We found in the study that there are variations in the wave climate of the Baltic Sea, which can be interpreted as being caused predominantly by a rotation of wind direction rather than increased wind speed, implying that associated variations in the airflow direction can be a dominant driver of regional climate changes.
The increase in atmospheric greenhouse gases (GHGs) is one of the main causes for the increase in global mean surface temperature. There is no good quantitative measure to determine when it is too late to start reducing GHGs in order to avoid dangerous anthropogenic interference. We develop a method for determining a so-called point of no return (PNR) for several GHG emission scenarios. The innovative element in this approach is the applicability to high-dimensional climate models.
We compare the latest observations of relative and specific humidity with those from climate models. The climate models do not accurately reproduce the observed humidity behaviour for the last 15–20 years. We use the temporal, spatial and trend information to contrast the patterns exhibited by the observations and models. The temporal behaviour of the observations has previously been documented and is consistent with faster warming rates over land compared to oceans.
Applying a global carbon tax on fossil was shown to lead to increased bioenergy production in four out of five scenarios. Increased bioenergy production led to global cropland changes that were up to 50 % larger by 2100 compared to the reference case (without global carbon tax). For scenarios with strong cropland expansion due to high population growth coupled with low technological change or bioenergy production, the biosphere was simulated to switch from a carbon sink into a carbon source.
Processes behind observed long-term variations in marine ecosystems are difficult to be deduced from in situ observations only. By statistically analysing a 61-year model simulation for the North Sea and Baltic Sea and additional model scenarios, we identified major modes of variability in the environmental variables and associated those with changes in primary production. We found that the dominant impact on changes in ecosystem productivity was introduced by modulations of the wind fields.
The deep waters of the Baltic Sea host an expanding dead zone, where low-oxygen conditions favour the natural production of two strong greenhouse gases, methane and nitrous oxide. Oxygen is introduced into the deeps only during rare salt pulses. We studied the effects of a recent salt pulse on Baltic greenhouse gas production. We found that where oxygen was introduced, methane was largely removed, while nitrous oxide production increased, indicating strong effects on greenhouse gas dynamics.
Benjamin M. Sanderson, Yangyang Xu, Claudia Tebaldi, Michael Wehner, Brian O'Neill, Alexandra Jahn, Angeline G. Pendergrass, Flavio Lehner, Warren G. Strand, Lei Lin, Reto Knutti, and Jean Francois Lamarque
We present the results of a set of climate simulations designed to simulate futures in which the Earth's temperature is stabilized at the levels referred to in the 2015 Paris Agreement. We consider the necessary future emissions reductions and the aspects of extreme weather which differ significantly between the 2 and 1.5 °C climate in the simulations.
We provide an explanation why land temperatures respond more strongly to global warming than ocean temperatures, a robust finding in observations and models that has so far not been understood well. We explain it by the different ways by which ocean and land surfaces buffer the strong variation in solar radiation and demonstrate this with a simple, physically based model. Our explanation also illustrates why nighttime temperatures warm more strongly, another robust finding of global warming.
For the first time, a climatology of Lyapunov exponents (FTLE) for the period 1979–2014 has been established. This climatology is able to reproduce the main large-scale structures observed in the troposphere. The mean FTLE has been shown to correlate with the baroclinic Eady growth rate within timescales of a few days. As a case study, the contribution of atmospheric rivers to this climatology and their contribution to rainfalls over the Sahara and UK regions have been studied.
Global cropland net primary production has tripled over the last 50 years. However, long-term comparisons across global croplands are scarce due to the lack of detailed management data. Here, we conducted a simulation study of global cropland production from 1961 to 2010 using the VEGAS model. We modified the key parameter associated with the Green Revolution. The updated results decreased the RMSE by ~ 45 %, suggesting it is important to calibrate key parameters on regional scales.
We present a methodology to adjust the systematic errors of climate-modeled temperature with a simultaneous long-term trend preservation. The method considers the normalization of the temperature towards a reference period modeled temperature and the estimation of a residual signal, in order to apply adjustment only to the former. The skill of the methodology is compared to other methods while also assessed on the European scale.