scholarly journals Estimating 750 years of temperature variations and uncertainties in the Pyrenees by tree-ring reconstructions and climate simulations

2012 ◽  
Vol 8 (3) ◽  
pp. 919-933 ◽  
Author(s):  
I. Dorado Liñán ◽  
U. Büntgen ◽  
F. González-Rouco ◽  
E. Zorita ◽  
J. P. Montávez ◽  
...  
Keyword(s):  
Tree Ring ◽  
Climate Model ◽  
Maximum Density ◽  
Positive Trend ◽  
Temperature Variations ◽  
Model Simulations ◽  
Mean Temperature ◽  
Climate Simulations ◽  
Temperature Reconstructions ◽  
Climate Model Simulations

Abstract. Past temperature variations are usually inferred from proxy data or estimated using general circulation models. Comparisons between climate estimations derived from proxy records and from model simulations help to better understand mechanisms driving climate variations, and also offer the possibility to identify deficiencies in both approaches. This paper presents regional temperature reconstructions based on tree-ring maximum density series in the Pyrenees, and compares them with the output of global simulations for this region and with regional climate model simulations conducted for the target region. An ensemble of 24 reconstructions of May-to-September regional mean temperature was derived from 22 maximum density tree-ring site chronologies distributed over the larger Pyrenees area. Four different tree-ring series standardization procedures were applied, combining two detrending methods: 300-yr spline and the regional curve standardization (RCS). Additionally, different methodological variants for the regional chronology were generated by using three different aggregation methods. Calibration verification trials were performed in split periods and using two methods: regression and a simple variance matching. The resulting set of temperature reconstructions was compared with climate simulations performed with global (ECHO-G) and regional (MM5) climate models. The 24 variants of May-to-September temperature reconstructions reveal a generally coherent pattern of inter-annual to multi-centennial temperature variations in the Pyrenees region for the last 750 yr. However, some reconstructions display a marked positive trend for the entire length of the reconstruction, pointing out that the application of the RCS method to a suboptimal set of samples may lead to unreliable results. Climate model simulations agree with the tree-ring based reconstructions at multi-decadal time scales, suggesting solar variability and volcanism as the main factors controlling preindustrial mean temperature variations in the Pyrenees. Nevertheless, the comparison also highlights differences with the reconstructions, mainly in the amplitude of past temperature variations and in the 20th century trends. Neither proxy-based reconstructions nor model simulations are able to perfectly track the temperature variations of the instrumental record, suggesting that both approximations still need further improvements.

scholarly journals Anthropogenic forcing and response yield observed positive trend in Earth’s energy imbalance

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shiv Priyam Raghuraman ◽  
David Paynter ◽  
V. Ramaswamy
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Solar Spectrum ◽  
Internal Variability ◽  
Satellite Observations ◽  
Positive Trend ◽  
Energy Imbalance ◽  
Model Simulations ◽  
Heat Uptake ◽  
Climate Model Simulations

AbstractThe observed trend in Earth’s energy imbalance (TEEI), a measure of the acceleration of heat uptake by the planet, is a fundamental indicator of perturbations to climate. Satellite observations (2001–2020) reveal a significant positive globally-averaged TEEI of 0.38 ± 0.24 Wm−2decade−1, but the contributing drivers have yet to be understood. Using climate model simulations, we show that it is exceptionally unlikely (<1% probability) that this trend can be explained by internal variability. Instead, TEEI is achieved only upon accounting for the increase in anthropogenic radiative forcing and the associated climate response. TEEI is driven by a large decrease in reflected solar radiation and a small increase in emitted infrared radiation. This is because recent changes in forcing and feedbacks are additive in the solar spectrum, while being nearly offset by each other in the infrared. We conclude that the satellite record provides clear evidence of a human-influenced climate system.

Reconciling the BDC response in climate models to the volcanic forcings with reanalyses

2020 ◽  
Author(s):  
Mohamadou Diallo ◽  
Hella Garny ◽  
Roland Eichinger ◽  
Valentina Aquila ◽  
Manfred Ern ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Model Simulations ◽  
Current Climate ◽  
Climate Simulations ◽  
Pinatubo Eruption ◽  
Speed Up ◽  
Stratospheric Circulation ◽  
Volcanic Aerosols ◽  
Climate Model Simulations

&lt;p&gt;The stratospheric Brewer--Dobson circulation (BDC) is an important element of climate system as it determines the concentration of radiatively active trace gases like water vapor, ozone and aerosol above the tropopause. Climate models predict that increasing greenhouse gas levels speed up the stratospheric circulation. BDC changes is substantially modulated by different modes of climate variability (QBO, ENSO, solar cycle), including the volcanic aerosols. However, such variability is often not reliably included or represented in current climate model simulations, challenging the evaluation of models&amp;#8217; behavior against observations and constituting a major uncertainty in current climate simulations.&amp;#160;&lt;/p&gt;&lt;p&gt;Here, we investigate the main differences between the reanalysis and the CCMI/CMIP6 climate models&amp;#8217; response to stratospheric volcanic forcings regarding the depth/strength of the stratospheric BDC, with a focus on potential changes in the deep and shallow circulation branches. We also discuss the key reasons of the discrepancies (incl. uncertainties associated with volcanological forcing datasets and missing direct aerosol heating in the reanalysis) in the BDC response between reanalysis-driven and climate model simulations in the lower, mid and upper stratosphere. Finally, we assess the dynamical mechanisms involved in the volcanically-induced BDC changes to understand the opposite regime between lower, middle and upper stratosphere after the Mt Pinatubo eruption.&lt;/p&gt;

scholarly journals Climate simulations and pollen data reveal the distribution and connectivity of temperate tree populations in eastern Asia during the Last Glacial Maximum

2020 ◽  
Vol 16 (6) ◽  
pp. 2039-2054
Author(s):  
Suzanne Alice Ghislaine Leroy ◽  
Klaus Arpe ◽  
Uwe Mikolajewicz ◽  
Jing Wu
Keyword(s):  
Climate Model ◽  
Deciduous Tree ◽  
Eastern Asia ◽  
Pollen Data ◽  
Model Simulations ◽  
Climate Simulations ◽  
Temperate Deciduous ◽  
Climate Model Simulations ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Publications on temperate deciduous tree refugia in Europe are abundant, but little is known about the patterns of temperate tree refugia in eastern Asia, an area where biodiversity survived Quaternary glaciations and which has the world's most diverse temperate flora. Our goal is to compare climate model simulations with pollen data in order to establish the location of glacial refugia during the Last Glacial Maximum (LGM). Limits in which temperate deciduous trees can survive are taken from the literature. The model outputs are first tested for the present by comparing climate models with published modern pollen data. As this method turned out to be satisfactory for the present, the same approach was used for the LGM. Climate model simulations (ECHAM5 T106), statistically further downscaled, are used to infer the temperate deciduous tree distribution during the LGM. These were compared with available fossil temperate tree pollen occurrences. The impact of the LGM on the eastern Asian climate was much weaker than on the European climate. The area of possible tree growth shifts only by about 2∘ to the south between the present and the LGM. This contributes to explaining the greater biodiversity of forests in eastern Asia compared to Europe. Climate simulations and the available, although fractional, fossil pollen data agree. Therefore, climate estimations can safely be used to fill areas without pollen data by mapping potential refugia distributions. The results show two important areas with population connectivity: the Yellow Sea emerged shelf and the southern Himalayas. These two areas were suitable for temperate deciduous tree growth, providing corridors for population migration and connectivity (i.e. less population fragmentation) in glacial periods. Many tree populations live in interglacial refugia, not glacial ones. The fact that the model simulation for the LGM fits so well with observed pollen distribution is another indication that the model used is good enough to also simulate the LGM period.

scholarly journals Polar amplification of Pliocene climate by elevated trace gas radiative forcing

2020 ◽  
Vol 117 (38) ◽  
pp. 23401-23407
Author(s):  
Peter O. Hopcroft ◽  
Gilles Ramstein ◽  
Thomas A. M. Pugh ◽  
Stephen J. Hunter ◽  
Fabiola Murguia-Flores ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Trace Gas ◽  
Geological Evidence ◽  
Model Simulations ◽  
Climate Simulations ◽  
Climate Model Simulations ◽  
Near Future ◽  
Middle Pliocene

Warm periods in Earth’s history offer opportunities to understand the dynamics of the Earth system under conditions that are similar to those expected in the near future. The Middle Pliocene warm period (MPWP), from 3.3 to 3.0 My B.P, is the most recent time when atmospheric CO2levels were as high as today. However, climate model simulations of the Pliocene underestimate high-latitude warming that has been reconstructed from fossil pollen samples and other geological archives. One possible reason for this is that enhanced non-CO2trace gas radiative forcing during the Pliocene, including from methane (CH4), has not been included in modeling. We use a suite of terrestrial biogeochemistry models forced with MPWP climate model simulations from four different climate models to produce a comprehensive reconstruction of the MPWP CH4cycle, including uncertainty. We simulate an atmospheric CH4mixing ratio of 1,000 to 1,200 ppbv, which in combination with estimates of radiative forcing from N2O and O3, contributes a non-CO2radiative forcing of 0.9W⋅m−2(range 0.6 to 1.1), which is 43% (range 36 to 56%) of the CO2radiative forcing used in MPWP climate simulations. This additional forcing would cause a global surface temperature increase of 0.6 to 1.0 °C, with amplified changes at high latitudes, improving agreement with geological evidence of Middle Pliocene climate. We conclude that natural trace gas feedbacks are critical for interpreting climate warmth during the Pliocene and potentially many other warm phases of the Cenezoic. These results also imply that using Pliocene CO2and temperature reconstructions alone may lead to overestimates of the fast or Charney climate sensitivity.

scholarly journals Technical Note: A diagnostic for ozone contributions of various NO<sub>x</sub> emissions in multi-decadal chemistry-climate model simulations

2004 ◽  
Vol 4 (1) ◽  
pp. 327-342 ◽  
Author(s):  
V. Grewe
Keyword(s):  
Error Analysis ◽  
Nitrogen Oxide ◽  
Climate Model ◽  
Technical Note ◽  
Nox Emission ◽  
Nox Emissions ◽  
Model Simulations ◽  
Linear Character ◽  
Climate Simulations ◽  
Climate Model Simulations

Abstract. Nitrogen oxide (NOx=NO+NO2) emissions from various sources contribute to the ozone budget. The identification of these contributions is important, e.g.  for the assessment of emissions from traffic. The non-linear character of ozone chemistry complicates the online diagnosis during multi-decadal chemistry-climate simulations. A methodology is suggested, which is efficient enough to be incorporated in multi-decadal simulations. Eight types of NOx emissions are included in the model. For each a NOy (=all N components, except N2 and N2O) tracer and an ozone tracer is included in the model, which experience the same emissions and loss processes like the online chemistry fields. To calculate the ozone changes caused by an individual NOx emission, the assumption is made that the NOx contributions from various sources are identical to the NOy contributions. To evaluate this method each NOx emission has been increased by 5% and a detailed error analysis is given. In the regions of the main impact of individual sources the potential error of the calculated contribution is significantly smaller than the contribution. Moreover, the changes caused by an increase of the emissions of 5% were detected with a higher accuracy than the potential errror of the absolut contribution.

scholarly journals The 1816 ‘year without a summer’ in an atmospheric reanalysis

2016 ◽  
Author(s):  
Philip Brohan ◽  
Gilbert P. Compo ◽  
Stefan Brönnimann ◽  
Robert J. Allan ◽  
Renate Auchmann ◽  
...  
Keyword(s):  
North America ◽  
Time Scales ◽  
Tree Ring ◽  
Climate Model ◽  
Stratospheric Aerosol ◽  
Model Simulations ◽  
Daily Weather ◽  
Food Shortages ◽  
Climate Model Simulations ◽  
Weather Impacts

Abstract. Two hundred years ago a very cold and wet summer devastated agriculture in Europe and North America, causing widespread food shortages, unrest and suffering – the "year without a summer". This is usually blamed on the eruption of Mount Tambora, in Indonesia, the previous April, but making a link between these two events has proven difficult, as the major impacts were at smaller space and time-scales than we can reconstruct with tree-ring observations and climate model simulations. Here we show that the very limited network of station barometer observations for the period is nevertheless enough to enable a dynamical atmospheric reanalysis to reconstruct the daily weather of summer 1816, over much of Europe. Adding stratospheric aerosol from the Tambora eruption to the reanalysis improves its reconstruction, explicitly linking the volcano to the weather impacts.

scholarly journals Tree-ring proxy based temperature reconstructions and climate model simulations: cross-comparison at the Pyrenees

2011 ◽  
Vol 7 (6) ◽  
pp. 3919-3957
Author(s):  
I. Dorado Liñán ◽  
U. Büntgen ◽  
F. González-Rouco ◽  
E. Zorita ◽  
J. P. Montávez ◽  
...  
Keyword(s):  
Tree Ring ◽  
Climate Models ◽  
Climate Model ◽  
Circulation Model ◽  
Last Millennium ◽  
Global Circulation Model ◽  
Northern Spain ◽  
Temperature Variations ◽  
Temperature Reconstructions ◽  
The Individual

Abstract. May-to-September mean temperatures over the larger Pyrenees area (Northern Spain and Southern France) are reconstructed for the last Millennium from 22 maximum density (MXD) tree-ring chronologies. For the standardization of the tree-ring series, two detrending methods (Regional Curve Standardization (RCS) and 300-yr spline) were combined with and without an adaptive power transform (PT) for variance stabilization in the individual series. Thus, four different standardization procedures were applied to the data. Additionally, different regional chronologies were generated by computing a mean composite, averaging the local chronologies, or by applying Principal Components Analysis (PCA) to extract common variance from the subsets of individual MXD chronologies. Calibration-verification trials were performed using the product of the three regional aggregation methods in split periods: 1900–1952 and 1953–2006. Two methods were used to calibrate the regional chronology: regression and a simple variance-matching, sometimes also known as composite-plus-scaling. The resulting set of temperature reconstructions was compared with climate simulations performed with global (ECHO-G over the last Millennium for the target region) and regional (MM5) climate models. The reconstructions reveal inter-annual to multi-centennial temperature variations at the Pyrenees region for the last 750 yr. Generally, variations at inter-decadal timescales, including the cold periods associated with the solar minima, are common to all reconstruction variants although some discrepancies are found at longer timescales. The simulations of the global circulation model ECHO-G and the regional model MM5 agree with the tree-ring based reconstructions at decadal to multi-decadal time-scales. However, the comparison also highlights differences that need to be understood, such as the amplitude of the temperature variations and the discrepancies regarding the 20th century trends.

scholarly journals Technical Note: A diagnostic for ozone contributions of various NO<sub>x</sub> emissions in multi-decadal chemistry-climate model simulations

2004 ◽  
Vol 4 (3) ◽  
pp. 729-736 ◽  
Author(s):  
V. Grewe
Keyword(s):  
Climate Model ◽  
Technical Note ◽  
Nox Emission ◽  
Nox Emissions ◽  
Model Simulations ◽  
Linear Character ◽  
Potential Error ◽  
Climate Simulations ◽  
Climate Model Simulations ◽  
Absolute Contribution

Abstract. Nitrogen oxide (NOx=NO+NO2) emissions from various sources contribute to the ozone budget. The identification of these contributions is important, e.g. for the assessment of emissions from traffic. The non-linear character of ozone chemistry complicates the online diagnosis during multi-decadal chemistry-climate simulations. A methodology is suggested, which is efficient enough to be incorporated in multi-decadal simulations. Eight types of NOx emissions are included in the model. For each a NOy (=all N components, except N2 and N2O) tracer and an ozone tracer is included in the model, which experience the same emissions and loss processes like the online chemistry fields. To calculate the ozone changes caused by an individual NOx emission, the assumption is made that the NOx relative contributions from various sources are identical to the NOy relative contributions. To evaluate this method each NOx emission has been increased by 5% and a detailed error analysis is given. In the regions of the main impact of individual sources the potential error of the calculated contribution is significantly smaller than the contribution. Moreover, the changes caused by an increase of the emissions of 5% were detected with a higher accuracy than the potential error of the absolute contribution.

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