Revisiting the existence of the global warming slowdown during the early 21st century

2021 ◽  
pp. 1-40
Keyword(s):  
Global Warming ◽  
Greenhouse Gas ◽  
Selection Bias ◽  
21St Century ◽  
Linear Trend ◽  
Warming Trend ◽  
Short Term ◽  
Early 21St Century ◽  
Decadal Scale ◽  
Global Temperature Change

Abstract There are heated debates on the existence of the global warming slowdown during the early 21st century. Although efforts have been made to clarify or reconcile the controversy over the issue, it is not explicitly addressed, restricting the understanding of global temperature change particularly under the background of increasing greenhouse-gas concentrations. Here, using extensive temperature datasets, we comprehensively reexamine the existence of the slowdown under all existing definitions during all decadal-scale periods spanning 1990-2017. Results show that the short-term linear-trend dependent definitions of slowdown make its identification severely suffer from the period selection bias, which largely explains the controversy over its existence. Also, the controversy is further aggravated by the significant impacts of the differences between various datasets on the recent temperature trend and the different baselines for measuring slowdown prescribed by various definitions. However, when the focus is shifted from specific periods to the probability of slowdown events, we find the probability is significantly higher in the 2000s than in the 1990s, regardless of which definition and dataset are adopted. This supports a slowdown during the early 21st century relative to the warming surge in the late 20th century, despite higher greenhouse-gas concentrations. Furthermore, we demonstrate that this decadal-scale slowdown is not incompatible with the centennial-scale anthropogenic warming trend, which has been accelerating since 1850 and never pauses or slows. This work partly reconciles the controversy over the existence of the warming slowdown and the discrepancy between the slowdown and anthropogenic warming.

scholarly journals Technical note: On comparing greenhouse gas emission metrics

2021 ◽  
Vol 21 (6) ◽  
pp. 4699-4708
Author(s):  
Ian Enting ◽  
Nathan Clisby
Keyword(s):  
Global Warming ◽  
Greenhouse Gas ◽  
Global Warming Potential ◽  
Radiative Forcing ◽  
Greenhouse Gas Emission ◽  
Technical Note ◽  
Short Term ◽  
Rates Of Change

Abstract. Many metrics for comparing greenhouse gas emissions can be expressed as an instantaneous global warming potential multiplied by the ratio of airborne fractions calculated in various ways. The forcing equivalent index (FEI) provides a specification for equal radiative forcing at all times at the expense of generally precluding point-by-point equivalence over time. The FEI can be expressed in terms of asymptotic airborne fractions for exponentially growing emissions. This provides a reference against which other metrics can be compared. Four other equivalence metrics are evaluated in terms of how closely they match the timescale dependence of FEI, with methane referenced to carbon dioxide used as an example. The 100-year global warming potential overestimates the long-term role of methane, while metrics based on rates of change overestimate the short-term contribution. A recently proposed metric based on differences between methane emissions 20 years apart provides a good compromise. Analysis of the timescale dependence of metrics expressed as Laplace transforms leads to an alternative metric that gives closer agreement with FEI at the expense of considering methane over longer time periods. The short-term behaviour, which is important when metrics are used for emissions trading, is illustrated with simple examples for the four metrics.

scholarly journals Changes in the biological productivity of the Russian Arctic land ecosystems in the 21st century

2021 ◽  
Vol 11 (1) ◽  
pp. 30-41
Author(s):  
A.A. Tishkov ◽  
◽  
E.A. Belonovskaya ◽  
A.N. Krenke ◽  
S.V. Titova ◽  
...  
Keyword(s):  
21St Century ◽  
Linear Trend ◽  
Field Measurements ◽  
Warming Trend ◽  
The Arctic ◽  
Russian Arctic ◽  
Production Forecast ◽  
Polar Urals ◽  
1960S And 1970S ◽  
The 1960S

The authors compare current productivity estimates with the data obtained in the 1960s and 1970s for the ecosystems of the Russian Arctic in the course of the International Biological Program. This makes it possible to identify objectively climate-related trends in their productivity in the 21st century. The authors used archives and current satellite data for the Russian Arctic, including AVHRR, LANDSAT, MODIS TERRA, and others, represented by periods of 30 years or more. They have revealed that by the 21st century, the phytomass stocks (reserves) of zonal ecosystems increased on average by 15—30%, and primary production by 10—15%. Compared with field measurements of the 1960—1970s at specific points, this growth reached 50% or more. In terms of productivity growth, the ecosystems of the Arctic European sector are leading, although in the 21st century the warming trend is not the highest here (0.4—0.5 °С/10 years). The production forecast of the Arctic land ecosystems for 2025 (deviation of the linear trend in comparison with 2000—2019) showed its continued growth in the Kola Peninsula, in the Bolshezemelmkaya tundra, the Yamal and Gydan Peninsulas, and a decrease in the Polar Urals, northern Siberia and Kolyma lowland. The growth of specific indicators of productivity in the 21st century reached a plateau and, similar to the warming case of the 1920—1940s, is unable to lead to zonal restructuring.

scholarly journals Strengthening of the hydrological cycle in future scenarios: atmospheric energy and water balance perspective

2012 ◽  
Vol 3 (2) ◽  
pp. 523-560 ◽  
Author(s):  
A. Alessandri ◽  
P. G. Fogli ◽  
M. Vichi ◽  
N. Zeng
Keyword(s):  
Global Warming ◽  
20Th Century ◽  
21St Century ◽  
Hydrological Cycle ◽  
Surface Fluxes ◽  
Mitigation Scenario ◽  
Budget Analysis ◽  
Large Perturbation ◽  
Decadal Scale ◽  
Global Precipitation

Abstract. Future climate scenarios experiencing global warming are expected to strengthen hydrological cycle during 21st century by comparison with the last decades of 20th century. We analyze strengthening of the global-scale increase in precipitation from the perspective of changes in whole atmospheric water and energy balances. Furthermore, by combining energy and water equations for the whole atmosphere we profitably obtain constraints for the changes in surface fluxes and for the partitioning at the surface between sensible and latent components. Above approach is applied to investigate difference in strengthening of hydrological cycle in two scenario centennial simulations performed with an Earth System model forced with specified atmospheric concentration pathways. Alongside the medium-high non-mitigation scenario SRES A1B, we considered a new aggressive-mitigation scenario (E1) with reduced fossil fuel use for energy production aimed at stabilizing global warming below 2 K. Quite unexpectedly, mitigation scenario is shown to strengthen hydrological cycle more than SRES A1B till around 2070. Our analysis shows that this is mostly a consequence of the larger increase in the negative radiative imbalance of atmosphere in E1 compared to A1B. This appears to be primarily related to the abated aerosol concentration in E1, which considerably reduces atmospheric absorption of solar radiation compared to A1B. In contrast, last decades of 21st century (21C) show marked increase of global precipitation in A1B compared to E1, despite the fact that the two scenarios display almost same overall increase of radiative imbalance with respect to 20th century. Our results show that radiative cooling is weakly effective in A1B throughout all 21C, so that two distinct mechanisms characterize the diverse strengthening of hydrological cycle in mid and end 21C. It is only through a very large perturbation of surface fluxes that A1B achieves larger increase of global precipitation in the last decades of 21C. Our energy/water budget analysis shows that this behavior is ultimately due to a bifurcation in the Bowen ratios change between the two scenarios. This work warns that mitigation policies, by abating aerosols, may lead to unexpected stronger intensification of hydrological cycle and associated changes that may last for decades after that global warming is effectively mitigated. On the other hand, it is here suggested that predictable components of the radiative forcing by aerosols may have the potential to effectively contribute to the decadal-scale predictability of changes in the hydrological strength.

scholarly journals Implications of potential future grand solar minimum for ozone layer and climate

2018 ◽  
Vol 18 (5) ◽  
pp. 3469-3483 ◽  
Author(s):  
Pavle Arsenovic ◽  
Eugene Rozanov ◽  
Julien Anet ◽  
Andrea Stenke ◽  
Werner Schmutz ◽  
...  
Keyword(s):  
Global Warming ◽  
Solar Activity ◽  
Greenhouse Gas ◽  
21St Century ◽  
Atmospheric Chemistry ◽  
Solar Minimum ◽  
Climate Model ◽  
Ozone Production ◽  
22Nd Century ◽  
The Impact

Abstract. Continued anthropogenic greenhouse gas (GHG) emissions are expected to cause further global warming throughout the 21st century. Understanding the role of natural forcings and their influence on global warming is thus of great interest. Here we investigate the impact of a recently proposed 21st century grand solar minimum on atmospheric chemistry and climate using the SOCOL3-MPIOM chemistry–climate model with an interactive ocean element. We examine five model simulations for the period 2000–2199, following the greenhouse gas concentration scenario RCP4.5 and a range of different solar forcings. The reference simulation is forced by perpetual repetition of solar cycle 23 until the year 2199. This reference is compared with grand solar minimum simulations, assuming a strong decline in solar activity of 3.5 and 6.5 W m−2, respectively, that last either until 2199 or recover in the 22nd century. Decreased solar activity by 6.5 W m−2 is found to yield up to a doubling of the GHG-induced stratospheric and mesospheric cooling. Under the grand solar minimum scenario, tropospheric temperatures are also projected to decrease compared to the reference. On the global scale a reduced solar forcing compensates for at most 15 % of the expected greenhouse warming at the end of the 21st and around 25 % at the end of the 22nd century. The regional effects are predicted to be significant, in particular in northern high-latitude winter. In the stratosphere, the reduction of around 15 % of incoming ultraviolet radiation leads to a decrease in ozone production by up to 8 %, which overcompensates for the anticipated ozone increase due to reduced stratospheric temperatures and an acceleration of the Brewer–Dobson circulation. This, in turn, leads to a delay in total ozone column recovery from anthropogenic halogen-induced depletion, with a global ozone recovery to the pre-ozone hole values happening only upon completion of the grand solar minimum.

Biochar production under low pyrolysis temperature leads to lesser overall global warming potential and greenhouse gas intensity under lowland and upland short-term condition

2020 ◽  
Author(s):  
Ronley Canatoy ◽  
Seung Tak Jeong ◽  
Pil Joo Kim
Keyword(s):  
Global Warming ◽  
Greenhouse Gas ◽  
Global Warming Potential ◽  
Soil Amendment ◽  
Pyrolysis Temperature ◽  
Ghg Emissions ◽  
Ghg Emission ◽  
Short Term ◽  
Greenhouse Gas Intensity ◽  
Upland Condition

<p>Biochar is a carbon-rich black stable solid substance that when utilized as soil amendment can effectively mitigate greenhouse gas (GHG) emission. However, during the pyrolysis process of organic feedstock (i.e. manure) greenhouse gases are released as the feedstock undergo thermochemical degradation. Many studies were reported with regards to the effectiveness of biochar to mitigate greenhouse gas emission and to maintain soil quality via carbon sequestration. However, no clear investigation was done regarding biochar utilization on reducing GHG emission in an integrated perspective that starts from pyrolysis (production) to field application (utilization). To evaluate the integrated influence of biochar utilization on the overall Global Warming Potential (GWP) and (Greenhouse Gas Intensity) GHGI at different temperature, the fluxes of GHGs during feedstock pyrolysis to soil application were calculated. The key components include GHGs released during production processes and biogenic GHG emissions taking place in the soil via short-term incubation experiment in lowland and upland condition treated with biochar pyrolyzed at different temperature. Highest pyrolysis temperature of 700<sup>o</sup>C emitted 6.92 Mg CO<sub>2</sub>-eq ton<sup>-1</sup> biochar, wherein 8.7% and 91.2% was contributed by Carbon dioxide (CO<sub>2</sub>) and Methane (CH<sub>4</sub>) effluxes, respectively, during pyrolysis. This GHG emission during pyrolysis at 700<sup>o</sup>C was 5.6, 2.2, and 1.5 times higher than at 400<sup>o</sup>C, 500<sup>o</sup>C and 600<sup>o</sup>C, respectively. Meanwhile, biochar produced at lowest temperature (Biochar400) when utilized as soil amendment emitted 43.4 and 38.2 Mg CO<sub>2</sub>-eq ha<sup>-1</sup> in lowland and upland condition, respectively. In addition, this emission value under lowland (and upland) condition was 1.38 (1.36), 1.51 (1.56) and 1.86 (1.91) times higher than Biochar500, Biochar600 and Biochar700, respectively. Combining the GWP during the production and the utilization processes in lowland and upland condition reveal that at 400<sup>o</sup>C emanates the lowest overall GWP of 93.3 and 88.1 Mg CO<sub>2</sub>-eq ha<sup>-1</sup>, respectively.  Moreover, under lowland (and upland) condition, overall GWP at 400<sup>o</sup>C was noted to be 65.7% (71.7%), 131.6% (140.4%) and 221.9% (237.1%), lower than at 500<sup>o</sup>C, 600<sup>o</sup>C and 700<sup>o</sup>C, respectively. In conclusion, the use of lower temperature during biomass pyrolysis and utilization of its derived biochar could be a practical approach to mitigate GHG emissions.</p><p> </p><p>Keywords: Biochar, Pyrolysis, Greenhouse gas, Methane, Global warming potential, Greenhouse gas intensity</p>

scholarly journals Historically unprecedented global glacier decline in the early 21st century

2015 ◽  
Vol 61 (228) ◽  
pp. 745-762 ◽  
Author(s):  
Michael Zemp ◽  
Holger Frey ◽  
Isabelle Gärtner-Roer ◽  
Samuel U. Nussbaumer ◽  
Martin Hoelzle ◽  
...  
Keyword(s):  
21St Century ◽  
Global Scale ◽  
Ice Age ◽  
Early 21St Century ◽  
Sea Level Fluctuations ◽  
Decadal Scale ◽  
The World ◽  
Global Sea Level ◽  
Monitoring Service ◽  
The Impact

AbstractObservations show that glaciers around the world are in retreat and losing mass. Internationally coordinated for over a century, glacier monitoring activities provide an unprecedented dataset of glacier observations from ground, air and space. Glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass-balance data relating to the impact that glaciers exercise on global sea-level fluctuations or on regional runoff. In this study we provide an overview and analysis of the main observational datasets compiled by the World Glacier Monitoring Service (WGMS). The dataset on glacier front variations (∼42 000 since 1600) delivers clear evidence that centennial glacier retreat is a global phenomenon. Intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the Little Ice Age (or Holocene). Glaciological and geodetic observations (∼5200 since 1850) show that the rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history, as indicated also in reconstructions from written and illustrated documents. This strong imbalance implies that glaciers in many regions will very likely suffer further ice loss, even if climate remains stable.

scholarly journals Radiative forcing and climate response to projected 21st century aerosol decreases

2015 ◽  
Vol 15 (6) ◽  
pp. 9293-9353 ◽  
Author(s):  
D. M. Westervelt ◽  
L. W. Horowitz ◽  
V. Naik ◽  
D. L. Mauzerall
Keyword(s):  
Global Warming ◽  
Greenhouse Gas ◽  
21St Century ◽  
Radiative Forcing ◽  
Cloud Droplet ◽  
Effective Radius ◽  
Climate Impacts ◽  
Climate Response ◽  
Aerosol Emission ◽  
Global Emissions

Abstract. It is widely expected that global emissions of atmospheric aerosols and their precursors will decrease strongly throughout the remainder of the 21st century, due to emission reduction policies enacted to protect human health. For instance, global emissions of aerosols and their precursors are projected to decrease by as much as 80% by the year 2100, according to the four Representative Concentration Pathway (RCP) scenarios. The removal of aerosols will cause unintended climate consequences, including an unmasking of global warming from long-lived greenhouse gases. We use the Geophysical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3) to simulate future climate over the 21st century with and without the aerosol emission changes projected by each of the RCPs in order to isolate the radiative forcing and climate response resulting from the aerosol reductions. We find that the projected global radiative forcing and climate response due to aerosol decreases do not vary significantly across the four RCPs by 2100, although there is some mid-century variation, especially in cloud droplet effective radius, that closely follows the RCP emissions and energy consumption projections. Up to 1 W m−2 of radiative forcing may be unmasked globally from 2005 to 2100 due to reductions in aerosol and precursor emissions, leading to average global temperature increases up to 1 K and global precipitation rate increases up to 0.09 mm d−1. Regionally and locally, climate impacts can be much larger, with a 2.1 K warming projected over China, Japan, and Korea due to the reduced aerosol emissions in RCP8.5, as well as nearly a 0.2 mm d−1 precipitation increase, a 7 g m−2 LWP decrease, and a 2 μm increase in cloud droplet effective radius. Future aerosol decreases could be responsible for 30–40% of total climate warming by 2100 in East Asia, even under the high greenhouse gas emissions scenario (RCP8.5). The expected unmasking of global warming caused by aerosol reductions will require more aggressive greenhouse gas mitigation policies than anticipated in order to meet desired climate targets.

scholarly journals Radiative forcing and climate response to projected 21st century aerosol decreases

2015 ◽  
Vol 15 (22) ◽  
pp. 12681-12703 ◽  
Author(s):  
D. M. Westervelt ◽  
L. W. Horowitz ◽  
V. Naik ◽  
J.-C. Golaz ◽  
D. L. Mauzerall
Keyword(s):  
Global Warming ◽  
Greenhouse Gas ◽  
21St Century ◽  
Radiative Forcing ◽  
Cloud Droplet ◽  
Effective Radius ◽  
Climate Impacts ◽  
Global Temperature ◽  
Climate Response ◽  
Global Emissions

Abstract. It is widely expected that global emissions of atmospheric aerosols and their precursors will decrease strongly throughout the remainder of the 21st century, due to emission reduction policies enacted to protect human health. For instance, global emissions of aerosols and their precursors are projected to decrease by as much as 80 % by the year 2100, according to the four Representative Concentration Pathway (RCP) scenarios. The removal of aerosols will cause unintended climate consequences, including an unmasking of global warming from long-lived greenhouse gases. We use the Geophysical Fluid Dynamics Laboratory Coupled Climate Model version 3 (GFDL CM3) to simulate future climate over the 21st century with and without the aerosol emission changes projected by each of the RCPs in order to isolate the radiative forcing and climate response resulting from the aerosol reductions. We find that the projected global radiative forcing and climate response due to aerosol decreases do not vary significantly across the four RCPs by 2100, although there is some mid-century variation, especially in cloud droplet effective radius, that closely follows the RCP emissions and energy consumption projections. Up to 1 W m−2 of radiative forcing may be unmasked globally from 2005 to 2100 due to reductions in aerosol and precursor emissions, leading to average global temperature increases up to 1 K and global precipitation rate increases up to 0.09 mm day−1. However, when using a version of CM3 with reduced present-day aerosol radiative forcing (−1.0 W m−2), the global temperature increase for RCP8.5 is about 0.5 K, with similar magnitude decreases in other climate response parameters as well. Regionally and locally, climate impacts can be much larger than the global mean, with a 2.1 K warming projected over China, Japan, and Korea due to the reduced aerosol emissions in RCP8.5, as well as nearly a 0.2 mm day−1 precipitation increase, a 7 g m−2 LWP decrease, and a 2 μm increase in cloud droplet effective radius. Future aerosol decreases could be responsible for 30–40 % of total climate warming (or 10–20 % with weaker aerosol forcing) by 2100 in East Asia, even under the high greenhouse gas emissions scenario (RCP8.5). The expected unmasking of global warming caused by aerosol reductions will require more aggressive greenhouse gas mitigation policies than anticipated in order to meet desired climate targets.

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