Global Mean Annual Temperature Research Articles

Determining confidence intervals in analyzing climatic series

In the context of the problem of global warming, the question of how much the observed increase in the mean air temperature over the last decades is likely due only to natural variability is studied. It is assumed that an observed temperature-data series of length N is a segment of a stationary random sequence with a spectrum known on an interval that does not include the lowest frequencies. The variance σ2(N) of the sample mean m* and the standard deviation σ(N), which determines the width of the confidence interval of m*, are calculated for different continuations of the spectrum to the low-frequency region. For a continuation of the spectrum that boundlessly increases, as does ω−2α (0 < α < 1/2) when the frequency ω tends to zero (red-noise spectrum), it is shown that, the closer the parameter α is to 1/2, the more slowly σ(N) tends to zero at N → ∞. Using an empirical spectrum of a global mean annual temperature series as an example, it is shown that the standard deviation significantly depends on the form of the spectrum in the lowest frequency region. An attempt has been made to assess the measure of standard-deviation uncertainty due to a lack of exact information on the spectrum in the low-frequency region. Important series characteristics—the equivalent number of independent observations N eq(N) and the time scale of correlation T 1(N) which are determined through the variance σ2(N) of m*—also depend on the form of the spectrum in the low-frequency region. For the red-noise spectrum, N eq(N) increases with an increase in N proportionally to N 1–2α (but not proportionally to N as in the case of bounded spectrum); the correlation scale T 1(N) is no longer constant (as in the case of bounded spectrum) and increases with an increase in N proportionally to N 2α.

Increasing impacts of climate change upon ecosystems with increasing global mean temperature rise

In a meta-analysis we integrate peer-reviewed studies that provide quantified estimates of future projected ecosystem changes related to quantified projected local or global climate changes. In an advance on previous analyses, we reference all studies to a common pre-industrial base-line for temperature, employing up-scaling techniques where necessary, detailing how impacts have been projected on every continent, in the oceans, and for the globe, for a wide range of ecosystem types and taxa. Dramatic and substantive projected increases of climate change impacts upon ecosystems are revealed with increasing annual global mean temperature rise above the pre-industrial mean (ΔTg). Substantial negative impacts are commonly projected as ΔTg reaches and exceeds 2°C, especially in biodiversity hotspots. Compliance with the ultimate objective of the United Nations Framework Convention on Climate Change (Article 2) requires that greenhouse gas concentrations be stabilized within a time frame “sufficient to allow ecosystems to adapt naturally to climate change”. Unless ΔTg is constrained to below 2°C at most, results here imply that it will be difficult to achieve compliance. This underscores the need to limit greenhouse gas emissions by accelerating mitigation efforts and by protecting existing ecosystems from greenhouse-gas producing land use change processes such as deforestation.

Sensitivity of a coupled climate-carbon cycle model to large volcanic eruptions during the last millennium

The sensitivity of the climate–biogeochemistry system to volcanic eruptions is investigated using the comprehensive Earth System Model developed at the Max Planck Institute for Meteorology. The model includes an interactive carbon cycle with modules for terrestrial biosphere as well as ocean biogeochemistry. The volcanic forcing is based on a recent reconstruction for the last 1200 yr. An ensemble of five simulations is performed and the averaged response of the system is analysed in particular for the largest eruption of the last millennium in the year 1258. After this eruption, the global annual mean temperature drops by 1 K and recovers slowly during 10 yr. Atmospheric CO2 concentration declines during 4 yr after the eruption by ca. 2 ppmv to its minimum value and then starts to increase towards the pre-eruption level. This CO2 decrease is explained mainly by reduced heterotrophic respiration on land in response to the surface cooling, which leads to increased carbon storage in soils, mostly in tropical and subtropical regions. The ocean acts as a weak carbon sink, which is primarily due to temperature-induced solubility. This sink saturates 2 yr after the eruption, earlier than the land uptake.

Global biogeophysical interactions between forest and climate

In two sensitivity experiments using the Earth System Model of the Max Planck Institute for Meteorology (MPI‐ESM), the vegetation cover of the ice‐free land surface has been set worldwide to either forest or grassland in order to quantify the quasi‐equilibrium response of the atmosphere and ocean components to extreme land surface boundary conditions. After 400 years of model integration, the global mean annual surface temperature increased by 0.7°K and declined by 0.6°K in the forest and grassland simulations, respectively, as compared to the control simulation. Thereafter, the geographic distribution of vegetation has been allowed to respond interactively to climate. After subsequent 500 years of interactive climate‐vegetation dynamics, both forest and grassland simulations converged to essentially the same climate state as in the control simulation. This convergence suggests an absence of multiple climate‐forest states in the current version of the MPI‐ESM.

Influence of volcanic activity on climate change in the past several centuries: Assessments with a climate model of intermediate complexity

The climate model of intermediate complexity developed at the A.M. Obukhov Institute of Atmospheric Physics of the Russian Academy of Sciences (IAP RAS CM) is supplemented by a scheme which takes into account the volcanic forcing of climate. With this model, ensemble experiments have been conducted for the 1600s–1900s, in which, along with the volcanic forcing, the anthropogenic forcing due to greenhouse gases and sulfate aerosols and the natural forcing due to variations in solar irradiance were taken into account. The model realistically reproduces the annual mean response of surface air temperature and precipitation to major eruptions both globally and regionally. In particular, the decreases in the annual mean global temperature Tg in the IAP RAS CM after the largest eruptions in the latter half of the 20th century, the Mt. Agung (1963), El Chichon (1982), and Mt. Pinatubo (1991) volcanic eruptions, are 0.28, 0.27, and 0.46 K, respectively, in agreement with estimates from observational data. Moreover, in the IAP RAS CM, the volcanic eruptions result in a general precipitation decrease, especially over land in the middle and high latitudes of the Northern Hemisphere. The seasonal distribution of the response shows good agreement with observations for high-latitude eruptions and worse agreement for tropical and subtropical volcanoes. On interdecadal scales, volcanism leads to variations in Tg on the order of 0.1 K. In numerical experiments with anthropogenic and natural forcings, the model reproduces a general change in surface air temperature over the past several centuries. Taking into account the volcanic forcing, along with that due to variations in solar irradiance, the model has partly reproduced the nonmonotonic global warming for the 20th century.

Pedogenic carbonate isotopes as evidence for extreme climatic events preceding the Triassic-Jurassic boundary: Implications for the biotic crisis?

Research Article| November 01, 2008 Pedogenic carbonate isotopes as evidence for extreme climatic events preceding the Triassic-Jurassic boundary: Implications for the biotic crisis? David M. Cleveland; David M. Cleveland 1Department of Geology, Baylor University, Waco, Texas 76798, USA †Present address: ExxonMobil Upstream Research Company, P.O. Box 2189, Houston, Texas 77252, USA; david.m.cleveland@exxonmobil.com. Search for other works by this author on: GSW Google Scholar Lee C. Nordt; Lee C. Nordt 1Department of Geology, Baylor University, Waco, Texas 76798, USA Search for other works by this author on: GSW Google Scholar Steve I. Dworkin; Steve I. Dworkin 1Department of Geology, Baylor University, Waco, Texas 76798, USA Search for other works by this author on: GSW Google Scholar Stacy C. Atchley Stacy C. Atchley 1Department of Geology, Baylor University, Waco, Texas 76798, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2008) 120 (11-12): 1408–1415. https://doi.org/10.1130/B26332.1 Article history received: 21 Sep 2007 rev-recd: 05 Feb 2008 accepted: 13 Feb 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David M. Cleveland, Lee C. Nordt, Steve I. Dworkin, Stacy C. Atchley; Pedogenic carbonate isotopes as evidence for extreme climatic events preceding the Triassic-Jurassic boundary: Implications for the biotic crisis?. GSA Bulletin 2008;; 120 (11-12): 1408–1415. doi: https://doi.org/10.1130/B26332.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Triassic-Jurassic boundary is associated with widespread marine and terrestrial extinctions, but there is disagreement regarding the existence and extent of climatic changes that may have driven the biotic crisis. Here, we apply quantitative isotopic climate proxies in order to construct two age-equivalent, relatively continuous temperature and pCO2 records that span the eight million years preceding the Triassic-Jurassic boundary and that supersede previous terrestrial records in temporal resolution. The δ18O data suggest that mean annual temperatures (MAT) increased by 7–9 °C from the late Norian to the Rhaetian in association with the peak increases in pCO2 levels. The δ13C data suggest relatively low late Norian pCO2 levels (<500–1000 ppmV), increased Rhaetian levels (>1500 ppmV), and at least two periods of extreme pCO2 levels (~3000 ppmV) preceding the Triassic-Jurassic boundary. These estimates are consistent with a recent Late Triassic climate model that suggests the effects of increased pCO2 levels on Pangea would cause severe climatic consequences, including a global MAT increase of 6 °C (>10 °C in some regions). While it is possible that periods of increased aridity could have resulted in erroneously high estimates of both temperature and pCO2 levels, it is likely that climate was still fluctuating during the end of the Triassic. Although our data precede the Triassic-Jurassic boundary, many studies conclude that the mass extinction took place over a more prolonged period beginning in the Late Triassic. Thus, climate may have been a significant driving mechanism of the Late Triassic extinctions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Introduction. Pliocene climate, processes and problems

Climate predictions produced by numerical climate models, often referred to as general circulation models (GCMs), suggest that by the end of the twenty-first century global mean annual surface air temperatures will increase by 1.1-6.4 degrees C. Trace gas records from ice cores indicate that atmospheric concentrations of CO2 are already higher than at any time during the last 650000 years. In the next 50 years, atmospheric CO2 concentrations are expected to reach a level not encountered since an epoch of time known as the Pliocene. Uniformitarianism is a key principle of geological science, but can the past also be a guide to the future? To what extent does an examination of the Pliocene geological record enable us to successfully understand and interpret this guide? How reliable are the 'retrodictions' of Pliocene climates produced by GCMs and what does this tell us about the accuracy of model predictions for the future? These questions provide the scientific rationale for this Theme Issue.

Model estimations of possible climatic changes in 21st century at different scenarios of solar and volcanic activities and anthropogenic impact

We have made estimations of climatic changes in the 21st century at different scenarios of changes in the solar and volcanic activities using ensemble calculations with the help of a three-dimensional climatic model taking the carbon cycle into account. This model was developed in the Oboukhov Institute of Atmo- spheric Physics, Russian Academy of Sciences. An ensemble of scenarios is used for possible changes of the solar radiation flux in the 21st century, based on different methods of extrapolation of the data for the period 1610-2000. Along with this, different scenarios of volcanic activity in the 21st century are used. The results of thus made calculations are indicative of a rather small role played by the solar activity variations in changes of the global mean annual near-surface temperature in the 21st century as compared to the expected anthropogenic impact. Model changes of the global near-surface temperature in the 21st century (possible variations of the solar radiation and volcanic activity included) are characterized by a general increase determined in the main by anthropogenic SRES scenarios.

State of the Climate in 2007

Abstract The combined land and ocean surface temperature in 2007 fell within the 10 highest on record, while the average land temperature was the warmest since global records began in 1880. In the low to midtroposphere, the annual global mean temperature was among the five warmest since reliable global records began in 1958, but still cooler than the record warmest year of 1998. For the fourth consecutive year, the annual precipitation averaged over global land surfaces was above the long-term mean, although the anomaly was significantly less than in 2006 when the annual value was the eighth wettest since 1901. The globally averaged concentration of carbon dioxide (CO2) continued to increase in 2007, having risen to 382.7 ppm at the Mauna Loa Observatory in Hawaii. The average rate of rise of CO2 has been 1.6 ppm yr−1 since 1980; however, since 2000 this has increased to 1.9 ppm yr−1. In addition, both methane (CH4) and carbon monoxide (CO) concentrations were also higher in 2007. Over the oceans, global ...

ABSTRACT

The combined land and ocean surface temperature in 2007 fell within the 10 highest on record, while the average land temperature was the warmest since global records began in 1880. In the low to midtroposphere, the annual global mean temperature was among the five warmest since reliable global records began in 1958, but still cooler than the record warmest year of 1998. For the fourth consecutive year, the annual precipitation averaged over global land surfaces was above the long-term mean, although the anomaly was significantly less than in 2006 when the annual value was the eighth wettest since 1901. The globally averaged concentration of carbon dioxide (CO2) continued to increase in 2007, having risen to 382.7 ppm at the Mauna Loa Observatory in Hawaii. The average rate of rise of CO2 has been 1.6 ppm yr−1 since 1980; however, since 2000 this has increased to 1.9 ppm yr−1. In addition, both methane (CH4) and carbon monoxide (CO) concentrations were also higher in 2007. Over the oceans, global SST during 2007 showed significant departures from the 1971–2000 climatology. Annual average upper-ocean heat content anomalies declined between 2006 and 2007 in the eastern equatorial Pacific and increased in off-equatorial bands in that ocean basin. These changes were consistent with the transition from an El Niño in 2006 to a La Niña in 2007. The global mean sea level anomaly (SLA) in 2007 was I.I mm higher than in 2006, which is about one standard deviation below what would be expected from the 15-yr trend value of 3.4 mm yr−1. In the tropics, the Atlantic hurricane season was near normal in 2007, although slightly more active than in 2006. In the north and south Indian Ocean Basins, both the seasonal totals and intensity of tropical cyclones (TC) were significantly above average, and included two Saffir-Simpson category 5 TCs in the north Indian Ocean and a world record rainfall amount of 5510 mm over a 3–8-day period on the island of Reunion in the south Indian Ocean. In the polar regions 2007 was the warmest on record for the Arctic, and continued a general, Arctic-wide warming trend that began in the mid-1960s. An unusually strong high pressure region in the Beaufort Sea during summer contributed to a record minimum Arctic sea ice cover in September. Measurements of the mass balance of glaciers and ice caps indicate that in most of the world, glaciers are shrinking in mass. The Greenland ice sheet experienced records in both the duration and extent of the summer surface melt. From the continental scale, as a whole the Antarctic was warmer than average in 2007, although the Antarctic Peninsula was considerably cooler than average. The size of the ozone hole was below the record levels of 2006, and near the average of the past 15 yr, due to warmer springtime temperatures in the Antarctic stratosphere.

Relationship between pesticide use and climate change for crops

The use (and abuse) of pesticides has increased to combat insect-pests and diseases. However, the major causes concern of are the undesirable side effects of these chemicals on biodiversity, environment, food quality and human health .Climate change will have important implications for insect conservation and pest status. Climate and weather can substantially influence the development and distribution of insects. Most of the warming over the last 50 years is likely to have been due to man-made activities. Anthropogenically induced climatic change arising from increasing levels of atmospheric greenhouse gases would, therefore, be likely to have a significant effect on agricultural insect pests. Current best estimates of changes in climate indicate an increase in global mean annual temperatures of 1[o] C by 2025 and 3[o]C by the end of the next century. Such increases in temperature have a number of implications for temperature-dependent insect pests. The Assessment investigates the relationship between pesticide use and climate for crops that require relatively large amounts of pesticide. This paper describes such input-driven agriculture, the problem of pests and diseases and the unsustainable agricultural practices that it leads to, and the socio-economic and health externalities resulting in farmer's distress in pesticide hot spots. To protect ourselves, our economy, and our land from the adverse effects of climate change, we must ultimately dramatically reduce emissions of carbon dioxide and other greenhouse gases. The causes of anthropogenic climate change are broad and often difficult to address. There is no single solution to this complex problem, but numerous opportunities exist for reducing problems of climate change. The issue of climate change is one of the most profound challenges of our time, and we believe it is a challenge that can be met.&#x0D; &#x0D; The Journal of AGRICULTURE AND ENVIRONMENT Vol. 8, 2007, pp. 83-91

Effects of historical land cover changes on climate

In order to explore the influence of anthropogenic land use on the climate system during the last millennium, a set of experiments is performed with an Earth system model of intermediate complexity—the McGill Paleoclimate Model (MPM-2). The present paper mainly focuses on biogeophysical effects of historical land cover changes. A dynamic scenario of deforestation is described based on changes in cropland fraction (RF99). The model simulates a decrease in global mean annual temperature in the range of 0.09–0.16°C, especially 0.14–0.22°C in Northern Hemisphere during the last 300 years. The responses of climate system to GHGs concentration changes are also calculated for comparisons. Now, afforestation is becoming an important choice for the enhancement of terrestrial carbon sequestration and adjustment of regional climate. The results indicate that biogeophysical effects of land cover changes cannot be neglected in the assessments of climate change.

A GEOCLIM simulation of climatic and biogeochemical consequences of Pangea breakup

Large fluctuations in continental configuration occur throughout the Mesozoic. While it has long been recognized that paleogeography may potentially influence atmospheric CO2 via the continental silicate weathering feedback, no numerical simulations have been done, because of the lack of a spatially resolved climate‐carbon model. GEOCLIM, a coupled numerical model of the climate and global biogeochemical cycles, is used to investigate the consequences of the Pangea breakup. The climate module of the GEOCLIM model is the FOAM atmospheric general circulation model, allowing the calculation of the consumption of atmospheric CO2 through continental silicate weathering with a spatial resolution of 7.5°long × 4.5°lat. Seven time slices have been simulated. We show that the breakup of the Pangea supercontinent triggers an increase in continental runoff, resulting in enhanced atmospheric CO2 consumption through silicate weathering. As a result, atmospheric CO2 falls from values above 3000 ppmv during the Triassic down to rather low levels during the Cretaceous (around 400 ppmv), resulting in a decrease in global mean annual continental temperatures from about 20°C to 10°C. Silicate weathering feedback and paleogeography both act to force the Earth system toward a dry and hot world reaching its optimum over the last 260 Myr during the Middle‐Late Triassic. In the super continent case, given the persistent aridity, the model generates high CO2 values to produce very warm continental temperatures. Conversely, in the fragmented case, the runoff becomes the most important contributor to the silicate weathering rate, hence producing a CO2 drawdown and a fall in continental temperatures. Finally, another unexpected outcome is the pronounced fluctuation in carbonate accumulation simulated by the model in response to the Pangea breakup. These fluctuations are driven by changes in continental carbonate weathering flux. Accounting for the fluctuations in area available for carbonate platforms, the simulated ratio of carbonate deposition between neritic and deep sea environments is in better agreement with available data.

Possible causes of the underestimation of paleoclimate low-frequency variability by statistical methods

The Northern Hemisphere mean surface temperature has shown a significant positive trend over the past two centuries. On the basis of the well-known reconstructions of global climate from proxy data, the conclusion is made that the current warming has been unprecedented during at least the past two millennia. On the other hand, it was demonstrated in [6] that the existing statistical models strongly underestimate the low-frequency variability of global annual mean temperature, thus making the conclusion drawn above questionable. At present, the results of [6] are interpreted as evidence that the Mann reconstruction is invalid [1]. To our knowledge, however, it is too early to draw such conclusions. What is the cause of smoothing low-frequency variability? To what extent are various statistical models used for paleoclimate reconstruction that is subject to this effect? To answer these questions, numerical experiments are performed with data sets of annual mean surface temperature over the past millennium that are simulated with the ECHO-G coupled ocean-atmosphere general circulation model.

Biogeophysical effects of historical land cover changes simulated by six Earth system models of intermediate complexity

Six Earth system models of intermediate complexity that are able to simulate interaction between atmosphere, ocean, and land surface, were forced with a scenario of land cover changes during the last millennium. In response to historical deforestation of about 18 million sq km, the models simulate a decrease in global mean annual temperature in the range of 0.13-0.25 degrees C. The rate of this cooling accelerated during the 19th century, reached a maximum in the first half of the 20th century, and declined at the end of the 20th century. This trend is explained by temporal and spatial dynamics of land cover changes, as the effect of deforestation on temperature is less pronounced for tropical than for temperate regions, and reforestation in the northern temperate areas during the second part of the 20th century partly offset the cooling trend. In most of the models, land cover changes lead to a decline in annual land evapotranspiration, while seasonal changes are rather equivocal because of spatial shifts in convergence zones. In the future, reforestation might be chosen as an option for the enhancement of terrestrial carbon sequestration. Our study indicates that biogeophysical mechanisms need to be accounted for in the assessment of land management options for climate change mitigation.

STATE OF THE CLIMATE IN 2004

Abstract From a global perspective, the annual average surface temperature in 2004 was the fourth highest value observed since regular instrumental records began in 1880. Global surface air temperatures in 2004 were 0.44°C (0.79°F) above the 1961–90 mean, according to both the U.S. and U.K. archives. Observations of the global annual mean temperature in 2004 from the combined lower and middle troposphere was 0.38°C (0.68°F)—the fourth warmest year in the 47-yr archive of worldwide radiosonde observations, and the ninth warmest year out of the past 26 based on satellite measurements. The average precipitation anomaly over global land areas in 2004 was 10.7 mm above average, which was ∼1% above the 1961–90 mean, and the first year since 2000 that the global mean value was wetter than average. Northern Hemisphere sea ice extent was the third lowest on record for the year, dating back to 1973. The annual snow cover extent over Northern Hemisphere land areas was 25.1 million km2, which was the 25th most extens...

Climate warming could reduce runoff significantly in New England, USA

The relation between mean annual temperature (MAT), mean annual precipitation (MAP) and evapotranspiration (ET) for 38 forested watersheds was determined to evaluate the potential increase in ET and resulting decrease in stream runoff that could occur following climate change and lengthening of the growing season. The watersheds were all predominantly forested and were located in eastern North America, along a gradient in MAT from 3.5 °C in New Brunswick, CA, to 19.8 °C in northern Florida. Regression analysis for MAT versus ET indicated that along this gradient ET increased at a rate of 2.85 cm °C −1 increase in MAT (±0.96 cm °C −1, 95% confidence limits). General circulation models (GCM) using current mid-range emission scenarios project global MAT to increase by about 3 °C during the 21st century. The inferred, potential, reduction in annual runoff associated with a 3 °C increase in MAT for a representative small coastal basin and an inland mountainous basin in New England would be 11–13%. Percentage reductions in average daily runoff could be substantially larger during the months of lowest flows (July–September). The largest absolute reductions in runoff are likely to be during April and May with smaller reduction in the fall. This seasonal pattern of reduction in runoff is consistent with lengthening of the growing season and an increase in the ratio of rain to snow. Future increases in water use efficiency (WUE), precipitation, and cloudiness could mitigate part or all of this reduction in runoff but the full effects of changing climate on WUE remain quite uncertain as do future trends in precipitation and cloudiness.

Pattern Scaling: An Examination of the Accuracy of the Technique for Describing Future Climates

A fully probabilistic, or risk, assessment of future regional climate changeand its impacts involves more scenarios of radiative forcing than can besimulated by a general (GCM) or regional (RCM) circulation model. Additionalscenarios may be created by scaling a spatial response pattern from a GCM bya global warming projection from a simple climate model. I examine thistechnique, known as pattern scaling, using a particular GCM (HadCM2).Thecritical assumption is that there is a linear relationship between the scaler(annual global-mean temperature) and the response pattern. Previous studieshave found this assumption to be broadly valid for annual temperature; Iextend this conclusion to precipitation and seasonal (JJA) climate. However,slight non-linearities arise from the dependence of the climatic response onthe rate, not just the amount, of change in the scaler. These non-linearitiesintroduce some significant errors into the estimates made by pattern scaling,but nonetheless the estimates accurately represent the modelled changes. Aresponse pattern may be made more robust by lengthening the period from whichit is obtained, by anomalising it relative to the control simulation, and byusing least squares regression to obtain it. The errors arising from patternscaling may be minimised by interpolating from a stronger to a weaker forcingscenario.

Constraining temperature variations over the last millennium by comparing simulated and observed atmospheric CO2

The response of atmospheric CO2 and climate to the reconstructed variability in solar irradiance and radiative forcing by volcanoes over the last millennium is examined by applying a coupled physical–biogeochemical climate model that includes the Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM) and a simplified analogue of a coupled atmosphere–ocean general circulation model. The modeled variations of atmospheric CO2 and Northern Hemisphere (NH) mean surface temperature are compatible with reconstructions from different Antarctic ice cores and temperature proxy data. Simulations where the magnitude of solar irradiance changes is increased yield a mismatch between model results and CO2 data, providing evidence for modest changes in solar irradiance and global mean temperatures over the past millennium and arguing against a significant amplification of the response of global or hemispheric annual mean temperature to solar forcing. Linear regression (r = 0.97) between modeled changes in atmospheric CO2 and NH mean surface temperature yields a CO2 increase of about 12 ppm for a temperature increase of 1 °C and associated precipitation and cloud cover changes. Then, the CO2 data range of 12 ppm implies that multi-decadal NH temperature changes between 1100 and 1700 AD had to be within 1 °C. Modeled preindustrial variations in atmospheric δ13C are small compared to the uncertainties in ice core δ13C data. Simulations with natural forcings only suggest that atmospheric CO2 would have remained around the preindustrial concentration of 280 ppm without anthropogenic emissions. Sensitivity experiments show that atmospheric CO2 closely follows decadal-mean temperature changes when changes in ocean circulation and ocean-sediment interactions are not important. The response in terrestrial carbon storage to factorial changes in temperature, the seasonality of temperature, precipitation, and atmospheric CO2 has been determined.

Extraordinary climates of Earth-like planets: three-dimensional climate simulations at extreme obliquity

A three-dimensional general-circulation climate model is used to simulate climates of Earth-like planets with extreme axial tilts (i.e. ‘obliquities’). While no terrestrial-planet analogue exists in the solar system, planets with steeply inclined spin axes may be common around nearby stars. Here we report the results of 12 numerical experiments with Earth-like planets having different obliquities (from 0° to 85°), continental geographies, and levels of the important greenhouse gas, CO2. Our simulations show intense seasonality in surface temperatures for obliquities [ges ]54°, with temperatures reaching 80–100 °C over the largest middle- and high-latitude continents around the summer solstice. Net annual warming at high latitudes is countered by reduced insolation and colder temperatures in the tropics, which maintains the global annual mean temperature of our planets to within a few degrees of 14 °C. Under reduced insolation, seasonal snow covers some land areas near the equator; however no significant net annual accumulation of snow or ice occurs in any of our runs with obliquity exceeding the present value, in contrast to some previous studies. None of our simulated planets were warm enough to develop a runaway greenhouse or cold enough to freeze over completely; therefore, most real Earth-like planets should be hospitable to life at high obliquity.