Northern Hemisphere Land Masses Research Articles

Fine-resolution mapping and assessment of artificial surfaces in the northern hemisphere permafrost environments

ABSTRACT Permafrost degradation has strong and long-lasting effects on anthropogenic land-use activities, contradicting the goal of sustainable development in polar and high-elevation regions. The artificial surface (AS) plays a central role in determining human-environment relationships in permafrost environments. Despite recent progress in monitoring land surfaces, attempts to map permafrost AS with satellite remote sensing have been limited. In this study, we propose an operational framework for fine-resolution mapping and assessment of permafrost AS across the entire Northern Hemisphere landmass. The proposed framework was designed to take advantage of prior knowledge obtained from existing global-scale land-cover products. As a result, a 10 m resolution permafrost AS map for 2016–2017 was created using a locally adaptive classification strategy. We found that the created map exhibited an overall accuracy of 91.7 ± 2.1% with minimum accuracies > 70%. We estimated that the total area of permafrost AS in the Northern Hemisphere was approximately 9,000 km2, most notably in the Russian Arctic. Future projections indicate that there will be over one-seventh of the permafrost AS area at high geohazard risk by the end of the twenty-first century. Our study provides new perspectives on the ‘permafrost-human-climate’ nexus, which can advance our understanding of the terrestrial system.

A regime shift in North Pacific annual mean sea surface temperature in 2013/14

This study revealed a new regime shift in the North Pacific annual mean sea surface temperature (SST) in 2013/14, robust in multiple SST data sets. This regime shift shows a horseshoe pattern with warming SST along the North American western coast and toward the Central Pacific. It suggests a phase reversal of the Victoria Mode (VM) and it seems unrelated to the shift in the Pacific Decadal Oscillation (PDO) and Interdecadal Pacific Oscillation (IPO). Associated with this regime shift, the annual surface air temperature significantly enhanced over the high-latitude landmass after 2014, whereas it declined over northeastern Canada and southwestern Greenland. The annual precipitation generally increased (decreased) in the Northern (Southern) Hemisphere landmass monsoon regions. There are no regime shifts in Equatorial Central-East Pacific SST and the intensity and locations of the Aleutian Low around 2013/14. These facts suggest the regime shift of North Pacific SST in 2013/14 may not originate from the decadal variations of the midlatitude atmosphere and tropical ocean. The extensive influence of this regime shift in 2013/14 on the atmospheric, oceanic and ecological systems warrants further investigation.

Holocene seasonal temperature evolution and spatial variability over the Northern Hemisphere landmass

The origin of the temperature divergence between Holocene proxy reconstructions and model simulations remains controversial, but it possibly results from potential biases in the seasonality of reconstructions or in the climate sensitivity of models. Here we present an extensive dataset of Holocene seasonal temperatures reconstructed using 1310 pollen records covering the Northern Hemisphere landmass. Our results indicate that both summer and winter temperatures warmed from the early to mid-Holocene (~11–7 ka BP) and then cooled thereafter, but with significant spatial variability. Strong early Holocene warming trend occurred mainly in Europe, eastern North America and northern Asia, which can be generally captured by model simulations and is likely associated with the retreat of continental ice sheets. The subsequent cooling trend is pervasively recorded except for northern Asia and southeastern North America, which may reflect the cross-seasonal impact of the decreasing summer insolation through climatic feedbacks, but the cooling in winter season is not well reproduced by climate models. Our results challenge the proposal that seasonal biases in proxies are the main origin of model–data discrepancies and highlight the critical impact of insolation and associated feedbacks on temperature changes, which warrant closer attention in future climate modelling.

Differences in snow-induced radiative forcing estimated from satellite and reanalysis surface albedo datasets over the Northern Hemisphere landmass for the overlapping period of 1982–2012

The snow-induced radiative forcing (SnRF) measures the instantaneous perturbation to Earth’s shortwave radiation at the top of the atmosphere (TOA) caused by the presence of snow cover. Land surface albedo (a s) is a key parameter in estimation of SnRF. Previous studies have focused on using satellite or reanalysis a s data in SnRF quantifications. However, their spatial and temporal differences remain unclear. In this study, SnRF over the Northern Hemisphere (NH) estimates from two satellite and four reanalysis a s datasets were compared for the overlapping period of 1982–2012. The 31-year annual-mean SnRF was estimated at −1.81 to −1.59 W m−2 from satellite a s datasets, with a peak of −4.01 W m−2 and Standard Deviation (SD) of 1.54 W m−2 in April. The comparable SnRF from reanalysis a s was −1.48 to −2.30 W m−2, with a peak of −4.77 W m−2 and SD of 0.81 W m−2 in the same month. In the seasonal cycle, SnRF from satellite a s displayed lower values from October to January, but higher values from February to July, compared with SnRF using reanalysis a s. Moreover, the annual-mean SnRF declined by 0.39–1.25 W m−2 during 1982–2012 from satellite a s datasets, which is much smaller than the results using reanalysis a s datasets. Furthermore, changes in monthly-mean SnRF from satellite a s displayed an enhance trend in snow accumulation seasons, which are largely different with the comparable changes from reanalysis-based SnRF, indicating that there are large interannual and intra-annual biases between SnRF estimates from satellite and reanalysis a s datasets. Based on above results, we conclude that the large discrepancies between SnRF estimations from satellite and reanalysis a s should be considered in evaluating the response and feedback of snow cover to Earth climate change in future studies, especially in radiation budget anomalies.

Human influence on joint changes in temperature, rainfall and continental aridity

Despite the pervasive impact of drought on human and natural systems, the large-scale mechanisms conducive to regional drying remain poorly understood. Here we use a multivariate approach1,2 to identify two distinct externally forced fingerprints from multiple ensembles of Earth system model simulations. The leading fingerprint, FM1(x), is characterized by global warming, intensified wet–dry patterns3 and progressive large-scale continental aridification, largely driven by multidecadal increases in greenhouse gas (GHG) emissions. The second fingerprint, FM2(x), captures a pronounced interhemispheric temperature contrast4,5, associated meridional shifts in the intertropical convergence zone6–9 and correlated anomalies in precipitation and aridity over California10, the Sahel11,12 and India. FM2(x) exhibits nonlinear temporal behaviour: the intertropical convergence zone moves southwards before 1975 in response to increases in hemispherically asymmetric sulfate aerosol emissions, and it shifts northwards after 1975 due to reduced sulfur dioxide emissions and the GHG-induced warming of Northern Hemisphere landmasses. Both fingerprints are statistically identifiable in observations of joint changes in temperature, rainfall and aridity during 1950–2014. We show that the reliable simulation of these changes requires combined forcing by GHGs, direct and indirect effects of aerosols, and large volcanic eruptions. Our results suggest that GHG-induced aridification may be modulated regionally by future reductions in sulfate aerosol emissions. Large-scale mechanisms causing regional drying are not well understood. Models and observational data reveal that human-caused changes in GHGs and aerosols led to detectable global and hemispheric signals in the joint behaviour of precipitation, temperature and aridity since the 1950s.

The Antarctic Parliamentarians Assembly - Diplomacy and Science

Dolan, P and Millwood Hargrave, M., The Antarctic Parliamentarians Assembly - Diplomacy and science. Geoscientist 30 (6), 24, 2020 https://doi.org/doi: 10.1144/geosci2020-094, Download the pdf here Peter Dolan (FGS) and Martyn Millwood Hargrave report on the inaugural Antarctic Parliamentarians Assembly, held in Westminster in December 2019 The inaugural Antarctic Parliamentarians Assembly was hosted by the UK government in London on 2 and 3 December 2019 to mark the 60th anniversary of the signing of the Antarctic Treaty and to discuss the future of the ‘White Continent’. Left: First year ice off the Royal Society Range, Scott Coast, Antarctica c. Martyn Millwood Hargrave Parliamentarians from 13 signatory countries, including most of the seven who claim sectors of Antarctica and other interested parties such as China, issued a final conference statement and press release, available at https://www.antarcticparliamentarians.com/download The meeting featured presentations on climate change, natural resources (primarily fishing), scientific research, geopolitics and tourism. (Since first drafting this report, COVID-19 is, of course, likely to severely limited tourism in the short to medium term.) But what were the ‘takeaways’? Global impact Despite its remote location, Antarctica has a global impact. This is partly because circum–Antarctic deep sea currents are connected to those in other oceans, affecting their path and nature. Changes in circulation in the south are, for example, predicted by fisheries experts to have a very negative impact on fish stocks in northern polar areas in years to come. Antarctica is both a victim and engine of change. These ocean currents contribute to climate change which in turn is driving the anomalous and rapid temperature increases being witnessed in West Antarctica. The melting of huge glacier systems (e.g. Thwaites and Pine island) and calving of ice shelves as a result of currently escalating CO2 emissions and global temperature increases are virtually certain to lead to global sea level rise of 30cm to 50cm over the next few decades. But here, Antarctica’s influence on the rest of the world arises again: whatever the sea level rise, it will be greatest in northern latitudes due to the gravitational pull of northern hemisphere landmasses. Coastal cities such as London, New Yorkand Shanghai, beware. So what to do? The parliamentarians and their advisors had no ‘silver bullets’ to offer. Their final statement “Noted with concern …the profound effects of climate change on Antarctica’s ecosystems and the potentially catastrophic effects of Antarctic ice loss on global sea level.” They agreed to: Uphold the Antarctic Treaty System. Establish the Assembly as a biennial gathering. Protect and conserve the Antarctic environment. Promote and support international scientific collaboration Ensure effective management of activities in Antarctica. Enthusiasm and concern We left enriched by the enthusiasm of the participants and the science but concerned at the inevitability of severe impacts from global sea level rise over our children’s lifetimes. There are many geoscience contributions we can make to mitigate the underlying drivers of climate change, and our profession and community should work hard to push these areas: CC(U)S, geothermal, facilitating efficiencies in the necessary harvesting of natural resources, etc. In the meantime, the buzzword from the environmental engineers was on increasing coastal resilience. It looks like we will all need it.

Asynchronous carbon sink saturation in African and Amazonian tropical forests.

Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions1-3. Climate-driven vegetation models typically predict that this tropical forest 'carbon sink' will continue for decades4,5. Here we assess trends in the carbon sink using 244 structurally intact African tropical forests spanning 11 countries, compare them with 321 published plots from Amazonia and investigate the underlying drivers of the trends. The carbon sink in live aboveground biomass in intact African tropical forests has been stable for the three decades to 2015, at 0.66 tonnes of carbon per hectare per year (95 per cent confidence interval 0.53-0.79), in contrast to the long-term decline in Amazonian forests6. Therefore the carbon sink responses of Earth's two largest expanses of tropical forest have diverged. The difference is largely driven by carbon losses from tree mortality, with no detectable multi-decadal trend in Africa and a long-term increase in Amazonia. Both continents show increasing tree growth, consistent with the expected net effect of rising atmospheric carbon dioxide and air temperature7-9. Despite the past stability of the African carbon sink, our most intensively monitored plotssuggest a post-2010 increase in carbon losses, delayed compared to Amazonia, indicating asynchronous carbon sink saturation on the two continents. A statistical model including carbon dioxide, temperature, drought and forest dynamics accounts for the observed trends and indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly. Overall, the uptake of carbon into Earth's intact tropical forests peaked in the 1990s. Given that the global terrestrial carbon sink is increasing in size, independent observations indicating greater recent carbon uptake into the Northern Hemisphere landmass10 reinforce our conclusion that the intact tropical forest carbon sink has already peaked. This saturation and ongoing decline of the tropical forest carbon sink has consequences for policies intended to stabilize Earth's climate.

Global warming hiatus contributed weakening of the Mascarene High in the Southern Indian Ocean

The Mascarene High (MH) is a semi-permanent subtropical high-pressure zone in the South Indian Ocean. Apart from its large influence on African and Australian weather patterns, it also helps in driving the inter-hemispheric circulation between the Indian Ocean in the south and subcontinental landmass in the north. Using observations and reanalysis products, this study for the first time investigates recent warming trend observed in the MH region during the Global Warming Hiatus (GWH) period (1998–2016). Significant positive trends are observed in sea surface temperature (SST), sea surface height (SSH) and oceanic heat content (OHC) during this period in the MH region. Mixed layer heat budget analysis reveals the dominant role of heat advection in the observed warming trend. During the GWH period, stronger zonal currents advect the warm waters from the Western Pacific (WP) towards the MH region via the Indonesian Throughflow (ITF). This warming in the MH reduces the sea level pressure therein and establishes a weak pressure gradient between the MH and the northern hemisphere landmass. This in-turn weakens the cross-equatorial winds in the western Indian Ocean.

Comparisons of Time Series of Annual Mean Surface Air Temperature for China since the 1900s: Observations, Model Simulations, and Extended Reanalysis

Abstract Time series of global or regional average surface air temperature (SAT) are fundamental to climate change studies. A number of studies have developed several national and regional SAT series for China, but because of the diversity of the meteorological observational sites, the different quality control routines for processing the data, and the inconsistency of the statistical methods used, they differ in their long-term trends. This paper assesses the similarities and differences of the existing time series of the annual average SAT for China that are based upon historical meteorological observations since the 1900s. The results indicate that the China average is similar to the series for the Northern Hemisphere (NH) landmass, except that the initial warming of the NH series derived from the CRUTEM3/4 datasets, which represent global historical land surface air temperatures and near-surface air temperature anomalies over land, respectively, ends earlier (before the early 1940s) than in China’s series. A major difference among the existing China average time series is the 1940s warmth, a period when there were very few observations across the country because of World War II. The SAT anomalies for China during the 1930s to 1940s have been reduced by improved homogeneity assessment compared to previous estimates. The new improved time series is in better agreement with both the historical twentieth-century reanalysis data and the historical climate simulation of phase 5 of the Coupled Model Intercomparison Project (CMIP5) models. The new time series also shows the slowdown of the warming trend during the past 18 yr (1998–2015). The best estimate of a linear trend for increases in temperature with a 95% uncertainty range is 0.121° ± 0.009°C decade–1 for 1900–2015, indicating that the improved homogeneity assessment for China leads to a slightly greater trend than that based on raw data (0.107° ± 0.009°C decade–1).

Diverse growth trends and climate responses across Eurasia’s boreal forest

The area covered by boreal forests accounts for ∼16% of the global and 22% of the Northern Hemisphere landmass. Changes in the productivity and functioning of this circumpolar biome not only have strong effects on species composition and diversity at regional to larger scales, but also on the Earth’s carbon cycle. Although temporal inconsistency in the response of tree growth to temperature has been reported from some locations at the higher northern latitudes, a systematic dendroecological network assessment is still missing for most of the boreal zone. Here, we analyze the geographical patterns of changes in summer temperature and precipitation across northern Eurasia >60 °N since 1951 AD, as well as the growth trends and climate responses of 445 Pinus, Larix and Picea ring width chronologies in the same area and period. In contrast to widespread summer warming, fluctuations in precipitation and tree growth are spatially more diverse and overall less distinct. Although the influence of summer temperature on ring formation is increasing with latitude and distinct moisture effects are restricted to a few southern locations, growth sensitivity to June–July temperature variability is only significant at 16.6% of all sites (p ≤ 0.01). By revealing complex climate constraints on the productivity of Eurasia’s northern forests, our results question the a priori suitability of boreal tree-ring width chronologies for reconstructing summer temperatures. This study further emphasizes regional climate differences and their role on the dynamics of boreal ecosystems, and also underlines the importance of free data access to facilitate the compilation and evaluation of massively replicated and updated dendroecological networks.

Projected 21st century changes in snow water equivalent over Northern Hemisphere landmasses from the CMIP5 model ensemble

Abstract. Changes in snow water equivalent (SWE) over Northern Hemisphere (NH) landmasses are investigated for the early (2016–2035), middle (2046–2065) and late (2080–2099) 21st century using a multi-model ensemble from 20 global climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The multi-model ensemble was found to provide a realistic estimate of observed NH mean winter SWE compared to the GlobSnow product. The multi-model ensemble projects significant decreases in SWE over the 21st century for most regions of the NH for representative concentration pathways (RCPs) 2.6, 4.5 and 8.5. This decrease is particularly evident over the Tibetan Plateau and North America. The only region with projected increases is eastern Siberia. Projected reductions in mean annual SWE exhibit a latitudinal gradient with the largest relative changes over lower latitudes. SWE is projected to undergo the largest decreases in the spring period where it is most strongly negatively correlated with air temperature. The reduction in snowfall amount from warming is shown to be the main contributor to projected changes in SWE during September to May over the NH.

Monitoring European average temperature based on the E‐OBS gridded data set

AbstractA European average temperature with monthly resolution is constructed based on the E‐OBS daily data set with near real‐time updates for monitoring. Taken together, the European average temperature and the associated gridded daily maps of surface temperature from the E‐OBS data set provide a detailed record of European climate variability and change since 1950. Both are based on validated station data provided by the European National Meteorological and Hydrological Services. A quantitative analysis of the uncertainty sources to the European average temperature indicates that the uncertainties due to urbanization, statistical interpolation, and the potential inhomogeneities in the input records to E‐OBS dominate the total uncertainty estimate. In the aggregation of the interpolation uncertainty from the daily to the monthly level and then to a European averaged value, the effective sample size and the effective spatial degrees of freedom are estimated to account for spatial and temporal coherency in the uncertainty estimates. The European average temperature shows that 7 years of the top 10 warmest years are from the period starting as recent as the year 2000 and a clear upward trend in annual average temperatures over the last few decades is visible. The most recent year in the top 10 coldest years is 1987. It also shows that warming in Europe is accelerating compared to the warming over the global land masses and to a lesser extent compared to the Northern Hemisphere land masses over the period 1980–2010.

On the persistent spread in snow-albedo feedback

Snow-albedo feedback (SAF) is examined in 25 climate change simulations participating in the Coupled Model Intercomparison Project version 5 (CMIP5). SAF behavior is compared to the feedback’s behavior in the previous (CMIP3) generation of global models. SAF strength exhibits a fivefold spread across CMIP5 models, ranging from 0.03 to 0.16 W m−2 K−1 (ensemble-mean = 0.08 W m−2 K−1). This accounts for much of the spread in 21st century warming of Northern Hemisphere land masses, and is very similar to the spread found in CMIP3 models. As with the CMIP3 models, there is a high degree of correspondence between the magnitudes of seasonal cycle and climate change versions of the feedback. Here we also show that their geographical footprint is similar. The ensemble-mean SAF strength is close to an observed estimate of the real climate’s seasonal cycle feedback strength. SAF strength is strongly correlated with the climatological surface albedo when the ground is covered by snow. The inter-model variation in this quantity is surprisingly large, ranging from 0.39 to 0.75. Models with large surface albedo when these regions are snow-covered will also have a large surface albedo contrast between snow-covered and snow-free regions, and therefore a correspondingly large SAF. Widely-varying treatments of vegetation masking of snow-covered surfaces are probably responsible for the spread in surface albedo where snow occurs, and the persistent spread in SAF in global climate models.

Northern Hemisphere geography of ice‐covered rivers

AbstractAlthough river ice is a major component of the cryosphere and is particularly important to many river processes, including extreme events, its full geographical coverage has never been documented. Recognizing that the freeze‐up and break‐up of river ice is closely linked to the timing of 0 °C air temperatures, this study analyses the spatial extent of river networks relative to the location of three 0 °C isotherm periods. These were defined to represent a suite of ice‐affected conditions that would be experienced for 6, 3 or 0·5 month periods, the briefest interval possibly leading only to a very thin and transient ice cover or simply border/frazil ice formation. Four different GIS databases were used to represent the river networks. The percentages of the total Northern Hemisphere land mass (average river network) influenced by cold temperatures conducive to ice formation were 52, 45 and 25 (56, 47 and 28), respectively. The related southern position of the isotherms ranged from 33°N, 35°N and 50°N in central North America to a nearly consistent 27°N for Eurasia, reflecting the influence of the high‐elevation central plateau region. Also identified are the lengths of major rivers that fall within the three 0 °C isotherm boundaries. Included are some of the world's largest rivers including the Lena, Mackenzie, Ob, Yellow, Yukon and Yenisey rivers, although their percentage of ice‐affected coverage varied for the three isotherm periods from a consistent 100% for the Lena and Yukon rivers to as little as 23% at the 6‐month interval for the Yellow River. Copyright © 2009 Her Majesty the Queen in right of Canada. Published by John Wiley & Sons, Ltd.

Controls on Northern Hemisphere snow albedo feedback quantified using satellite Earth observations

Observation based estimates of controls on snow albedo feedback (SAF) are needed to constrain the snow and albedo parameterizations in general circulation model (GCM) projections of air temperature over the Northern Hemisphere (NH) landmass. The total April‐May NH SAF, corresponding to the sum of the effect of temperature on surface albedo over snow covered surfaces (‘metamorphism’) and over surfaces transitioning from snow covered to snow free conditions (‘snow cover’), is derived with daily NH snow cover and surface albedo products using Advanced Very High Resolution Radiometer Polar Pathfinder satellite data and surface air temperature from ERA40 reanalysis data between 1982–1999. Without using snow cover information, the estimated total SAF, for land surfaces north of 30°N, of −0.93 ± 0.06%K−1 was not significantly different (95% confidence) from estimates based on International Satellite Cloud Climatology Project surface albedo data. The SAF, constrained to only snow covered areas, grew to −1.06 ± 0.08%K−1 with similar magnitudes for the ‘snow cover’ and ‘metamorphosis’ components. The SAF pattern was significantly correlated with the ‘snow cover’ component pattern over both North America and Eurasia but only over Eurasia for the ‘metamorphosis’ component. However, in contrast to GCM model based diagnoses of SAF, the control on the ‘snow cover’ component related to the albedo contrast of snow covered and snow free surfaces was not strongly correlated to the total SAF.

Biogeographical affinities of Late Cretaceous continental tetrapods of Europe: a review

Abstract The continental tetrapod assemblages from the Santonian-Maastrichtian of Europe consist of dinosaurs (theropods: Abelisauroidea, Alvarezsauridae, Dromaeosauridae, ?Oviraptorosauria, ?Troodontidae, and birds: Enantiornithes, basal Ornithurae; sauropods: Titanosauria; ankylosaurs: Nodosauridae; ornithopods: Hadrosauridae, Rhabdodontidae; and neoceratopsians), pterosaurs (Azhdarchidae), crocodyliforms (eusuchians: Alligatoroidea, Gavialoidea, ?Hylaeochampsidae; sebecosuchian-like ziphosuchians; and, probably, basal neosuchians), choristoderes (?Champsosauridae), squamates (lacertilians: Iguanidae s.l., Paramacellodidae, Polyglyphanodontinae, Varanoidea; snakes: Madtsoiidae; possible amphisbaenians), turtles (cryptodires: Chelydroidea, Kallokibotionidae, Solemydidae; pleurodires: Bothremydidae, Dortokidae), lissamphibians (Albanerpetontidae; anurans: Discoglossidae, Palaeobatrachidae; caudates: Batrachosauroididae, Salamandridae), and mammals (multituberculates: Kogaionidae, ?“Paracimexomys group”; marsupials: Herpetotheriidae; eutherians: “Zhelestidae”). The palaeobiogeographical affinities of the Late Cretaceous continental tetrapods of Europe are complex. The faunas are commonly considered to show a mixed pattern resulting from the addition of “Asiamerican” and Gondwanan forms to European taxa. Albanerpetontids, both paramacellodid and polyglyphonodontine lizards, and hadrosaurid dinosaurs are taxa with Palaeolaurasian (or, in some case, even Neopangean) affinities. Other forms, such as paleobatrachid and batrachosauroidid lissamphibians, solemydid turtles, alligatoroid crocodyliforms, and nodosaurid dinosaurs can be considered as Euramerican taxa. Kallokibotionid and dortokid turtles, rhabdodontid dinosaurs and kogaionid mammals are endemic to Europe. The Gondwanan taxa have been regarded as African immigrants that reached southern Europe via the Mediterranean Tethyan sill. Abelisaurid and titanosaurid dinosaurs, trematochampsid crocodyliforms, podocnemidid and bothremydid turtles, and boid and madtsoiid snakes constitute the basic pattern of the so-called “Eurogondwanan fauna”. However, the validity of some of these taxa is a disputed matter (Titanosauridae, Trematochampsidae), and the presence of other taxa in the Late Cretaceous of Europe is based on controversial data (Boidae, Podocnemididae). Only Abelisauroidea, Madtsoiidae and Bothremydidae (and, yet for confirming, Sebecosuchia) provide evidence of interchanges between Africa and Europe. At least abelisauroids might have reached Europe before the Late Cretaceous. In conclusion, most of the continental tetrapod taxa from the latest Cretaceous of Europe show affinities with those of northern Hemisphere landmasses. Latest Cretaceous trans-Tethyan dispersal events between Africa and Europe remain poorly documented.

Geoengineering climate by stratospheric sulfur injections: Earth system vulnerability to technological failure

We use a coupled climate-carbon cycle model of intermediate complexity to investigate scenarios of stratospheric sulfur injections as a measure to compensate for CO2-induced global warming. The baseline scenario includes the burning of 5,000 GtC of fossil fuels. A full compensation of CO2-induced warming requires a load of about 13 MtS in the stratosphere at the peak of atmospheric CO2 concentra- tion. Keeping global warming below 2 ◦ C reduces this load to 9 MtS. Compensation of CO2 forcing by stratospheric aerosols leads to a global reduction in precipitation, warmer winters in the high northern latitudes and cooler summers over northern hemisphere landmasses. The average surface ocean pH decreases by 0.7, reducing the calcifying ability of marine organisms. Because of the millennial persistence of the fossil fuel CO2 in the atmosphere, high levels of stratospheric aerosol loading would have to continue for thousands of years until CO2 was removed from the atmosphere. A termination of stratospheric aerosol loading results in abrupt global warming of up to 5 ◦ C within several decades, a vulnerability of the Earth system to technological failure.

Multi‐model decadal potential predictability of precipitation and temperature

A first multi‐model estimate of the long timescale potential predictability of precipitation is obtained based on over 8000 years of data from the control simulations of 21 state‐of‐the‐art coupled climate models. The analysis also updates earlier estimates of the potential predictability of temperature to provide a consistent estimate for these basic climate parameters. Long timescale potential predictability is found mainly over the oceans at middle to high latitudes and predominantly where the surface is connected to the deeper ocean. Precipitation's modest potential predictability resembles an attenuated version of that for temperature on these timescales. Over land, predictability is largely absent for precipitation and comparatively weak for temperature where it is found over the northern and western parts of northern hemisphere land masses bordering the oceans. Regions exhibiting potential predictability indicate where we may hope to find predictive skill at long timescales and also points indirectly to the processes involved.

High‐latitude eruptions cast shadow over the African monsoon and the flow of the Nile

Nile River records indicate very low flow following the 1783–1784 Laki volcanic eruption, as well as after other high‐latitude volcanic eruptions. As shown by climate model simulations of the Laki eruption, significant cooling (−1° to −3°C) of the Northern Hemisphere land masses during the boreal summer of 1783 resulted in a strong dynamical effect of weakening the African and Indian monsoon circulations, with precipitation anomalies of −1 to −3 mm/day over the Sahel of Africa, thus producing the low Nile flow. Future high‐latitude eruptions would significantly impact the food and water supplies in these areas. Using observations of the flow of the Nile River, this new understanding is used to support a date of 939 for the beginning of the eruption of the Eldgjá volcano in Iceland, the largest high‐latitude eruption of the past 1500 years.

Using the current seasonal cycle to constrain snow albedo feedback in future climate change

Differences in simulations of climate feedbacks are sources of significant divergence in climate models' temperature response to anthropogenic forcing. Snow albedo feedback is particularly critical for climate change prediction in heavily‐populated northern hemisphere land masses. Here we show its strength in current models exhibits a factor‐of‐three spread. These large intermodel variations in feedback strength in climate change are nearly perfectly correlated with comparably large intermodel variations in feedback strength in the context of the seasonal cycle. Moreover, the feedback strength in the real seasonal cycle can be measured and compared to simulated values. These mostly fall outside the range of the observed estimate, suggesting many models have an unrealistic snow albedo feedback in the seasonal cycle context. Because of the tight correlation between simulated feedback strength in the seasonal cycle and climate change, eliminating the model errors in the seasonal cycle will lead directly to a reduction in the spread of feedback strength in climate change. Though this comparison to observations may put the models in an unduly harsh light because of uncertainties in the observed estimate that are difficult to quantify, our results map out a clear strategy for targeted observation of the seasonal cycle to reduce divergence in simulations of climate sensitivity.