scholarly journals Potential Roles of Climate Feedback, Ocean Vertical Mixing and Overturning Circulation in Mitigating Global Warming

2021 ◽  
Author(s):  
Haijun Yang ◽  
Qiangzi Yang ◽  
Yang Li ◽  
Xiangying Zhou
Keyword(s):  
Global Warming ◽  
Decadal Variability ◽  
Vertical Mixing ◽  
Warming Trend ◽  
Climate Feedback ◽  
Overturning Circulation ◽  
Surface Warming ◽  
Long Run ◽  
The Pacific ◽  
Warming Hiatus

Abstract Despite the rapid increase of greenhouse gases (GHGs) in the atmosphere during the past 50 years, observed global mean surface temperature (GMST) showed a pause in the warming trend during the first decade of the twenty-first century. This is referred to as the global warming “hiatus.” A dominant hypothesis emphasizes that the superimposition of the cold phase of the Pacific decadal variability and the global warming trend can lead to the hiatus. This also implies a future acceleration of global warming once the Pacific decadal variability enters its warm phase. Using simply energy balance model, we explore three potential mechanisms that may restrain the GMST warming trend: enhanced negative climate feedback, downward ocean vertical mixing and overturning circulation. Forced by linearly increasing heating, a stronger negative climate feedback can reduce the GMST warming rate, but cannot result in a warming hiatus. Although the global overall climate feedback can be assumed to be more negative theoretically, in reality this feedback is likely to become more positive, which would potentially result in a disastrous runaway climate in several decades. Enhanced downward mixing of heat can cause a short-lived hiatus of surface warming rate, but this would eventually accelerate the surface warming in the long run. A stronger overturning circulation can transport more surface warm water downward just temporarily, which cannot stop the warming trend. This study suggests that in the long run, the only route to contain the global warming effectively is to reduce the GHGs.

scholarly journals Pacific variability reconciles observed and modelled global mean temperature increase since 1950

2020 ◽  
Author(s):  
Martin B. Stolpe ◽  
Kevin Cowtan ◽  
Iselin Medhaug ◽  
Reto Knutti
Keyword(s):  
Global Warming ◽  
Temperature Change ◽  
Temperature Increase ◽  
Global Temperature ◽  
Global Mean Temperature ◽  
Mean Temperature ◽  
The Pacific ◽  
Global Warming Hiatus ◽  
Warming Hiatus ◽  
Global Mean

Abstract Global mean temperature change simulated by climate models deviates from the observed temperature increase during decadal-scale periods in the past. In particular, warming during the ‘global warming hiatus’ in the early twenty-first century appears overestimated in CMIP5 and CMIP6 multi-model means. We examine the role of equatorial Pacific variability in these divergences since 1950 by comparing 18 studies that quantify the Pacific contribution to the ‘hiatus’ and earlier periods and by investigating the reasons for differing results. During the ‘global warming hiatus’ from 1992 to 2012, the estimated contributions differ by a factor of five, with multiple linear regression approaches generally indicating a smaller contribution of Pacific variability to global temperature than climate model experiments where the simulated tropical Pacific sea surface temperature (SST) or wind stress anomalies are nudged towards observations. These so-called pacemaker experiments suggest that the ‘hiatus’ is fully explained and possibly over-explained by Pacific variability. Most of the spread across the studies can be attributed to two factors: neglecting the forced signal in tropical Pacific SST, which is often the case in multiple regression studies but not in pacemaker experiments, underestimates the Pacific contribution to global temperature change by a factor of two during the ‘hiatus’; the sensitivity with which the global temperature responds to Pacific variability varies by a factor of two between models on a decadal time scale, questioning the robustness of single model pacemaker experiments. Once we have accounted for these factors, the CMIP5 mean warming adjusted for Pacific variability reproduces the observed annual global mean temperature closely, with a correlation coefficient of 0.985 from 1950 to 2018. The CMIP6 ensemble performs less favourably but improves if the models with the highest transient climate response are omitted from the ensemble mean.

Impact of the Pacific mean SST bias to the Atlantic-Pacific teleconnection

2020 ◽  
Author(s):  
Chen Li ◽  
Dietmar Dommenget ◽  
Shayne McGregor
Keyword(s):  
Decadal Variability ◽  
Atmospheric Stability ◽  
Low Frequency ◽  
Trade Wind ◽  
Atmospheric Teleconnection ◽  
Surface Warming ◽  
Sst Bias ◽  
Pacific Decadal Variability ◽  
The Pacific ◽  
Low Frequency Variability

<p><span>A robust eastern tropical Pacific surface temperature cooling trend along with the strengthening of Pacific trade wind is evident across different observations since late 1990s, which is considered as a pronounced contributor to the slowdown in global surface warming. However, most CMIP5 historical simulations failed to reproduce this La Ni</span>ñ<span>a-like change. Previous studies have attributed this discrepancy between the multi-model simulations and the observations to the underrepresentation of Pacific low-frequency variability together with the misrepresentation of inter-basin forcing response. The underlying reasons remain unclear. Here, we investigate a hypothesis that common Pacific mean SST bias may diminish the Pacific-Atlantic atmospheric teleconnection and further contribute to the underestimated eastern Pacific cooling. Model results suggest that the CMIP5-like Pacific bias acts to reduce the Atlantic heating response by strengthening the atmospheric stability over the Atlantic region and therefore weaken the trans-basin variability. In addition, </span>the Pacific bias simulation with a strong SST cold tongue substantially undermined the positive zonal wind feedback, which also contributes to the underestimated Pacific cooling response. Future efforts aim at reducing the model mean state biases may significantly help to improve the simulation skills of the trans-basin teleconnection, Pacific decadal variability, and the associated Pacific dynamics.      </p>

scholarly journals Unraveling Causes for the Changing Behavior of the Tropical Indian Ocean in the Past Few Decades

2018 ◽  
Vol 31 (6) ◽  
pp. 2377-2388 ◽  
Author(s):  
Lei Zhang ◽  
Weiqing Han ◽  
Frank Sienz
Keyword(s):  
Indian Ocean ◽  
Time Scales ◽  
Climate Models ◽  
Decadal Variability ◽  
Global Climate ◽  
Tropical Indian Ocean ◽  
Volcanic Eruptions ◽  
Warming Trend ◽  
External Forcing ◽  
The Pacific

Observations show that decadal (10–20 yr) to interdecadal (>20 yr) variability of the tropical Indian Ocean (TIO) sea surface temperature (SST) closely follows that of the Pacific until the 1960s. Since then, the TIO SST exhibits a persistent warming trend, whereas the Pacific SST shows large-amplitude fluctuations associated with the interdecadal Pacific oscillation (IPO), and the decadal variability of the TIO SST is out of phase with that of the Pacific after around 1980. Here causes for the changing behavior of the TIO SST are explored, by analyzing multiple observational datasets and the recently available large-ensemble simulations from two climate models. It is found that on interdecadal time scales, the persistent TIO warming trend is caused by emergence of anthropogenic warming overcoming internal variability, while the time of emergence occurs much later in the Pacific. On decadal time scales, two major tropical volcanic eruptions occurred in the 1980s and 1990s causing decadal SST cooling over the TIO during which the IPO was in warm phase, yielding the out-of-phase relation. The more evident fingerprints of external forcing in the TIO compared to the Pacific result from the much weaker TIO internal decadal–interdecadal variability, making the TIO prone to the external forcing. These results imply that the ongoing warming and natural external forcing may make the Indian Ocean more active, playing an increasingly important role in affecting regional and global climate.

scholarly journals Tracking the Missing Heat from the Global Warming Hiatus

Eos ◽  
2015 ◽  
Vol 96 ◽  
Author(s):  
Christina Reed
Keyword(s):  
Global Warming ◽  
Pacific Ocean ◽  
Indian Ocean ◽  
Surface Heat ◽  
The Pacific ◽  
Global Warming Hiatus ◽  
The Indian Ocean ◽  
The Pacific Ocean ◽  
Warming Hiatus

Despite indications that the Pacific Ocean is helping to take up the world's missing surface heat, it is not storing the heat; oceanographers now find the ocean has moved heat over to the Indian Ocean.

scholarly journals On the Mechanisms of Pacific Decadal Oscillation Modulation in a Warming Climate

2019 ◽  
Vol 32 (5) ◽  
pp. 1443-1459 ◽  
Author(s):  
Tao Geng ◽  
Yun Yang ◽  
Lixin Wu
Keyword(s):  
Growth Rate ◽  
Global Warming ◽  
Pacific Decadal Oscillation ◽  
Decadal Variability ◽  
Coupled Model ◽  
Growth Time ◽  
Coupled Mode ◽  
Warming Climate ◽  
The Pacific ◽  
Intercomparison Project

Abstract Changes of the Pacific decadal oscillation (PDO) under global warming are investigated by using outputs from phase 5 of the Coupled Model Intercomparison Project (CMIP5) and a theoretical midlatitude air–sea coupled model. In a warming climate, the decadal variability of the PDO is found to be significantly suppressed, with the amplitude reduced and the decadal cycle shifted toward a higher-frequency band. We used the theoretical model put forward by Goodman and Marshall (herein the GM model) to underpin the potential mechanisms. The GM model exhibits a growing coupled mode that resembles the simulated PDO. It is found that the suppression of the PDO appears to be associated with the acceleration of Rossby waves due to the enhanced oceanic stratification under global warming. This shortens the PDO period and reduces PDO amplitude by limiting the growth time of the coupled mode. The GM model also suggests that the increase of growth rate due to strengthening of oceanic stratification tends to magnify the PDO amplitude, counteracting the Rossby wave effect. This growth rate influence, however, plays a secondary role.

The Pacific Decadal Oscillation less predictable under greenhouse warming

2020 ◽  
Author(s):  
Shujun Li
Keyword(s):  
Pacific Decadal Oscillation ◽  
Decadal Variability ◽  
Coupled Model ◽  
Influential Factor ◽  
Growth Time ◽  
Greenhouse Warming ◽  
Surface Warming ◽  
The North ◽  
Global Mean Temperature ◽  
The Pacific

<p><strong>The Pacific Decadal Oscillation (PDO) is the most prominent form of decadal variability over the North Pacific, characterized by its horseshoe-like sea surface temperature (SST) anomaly pattern. The PDO exerts a substantial influence on marine ecosystems, fisheries, and agriculture. Through modulating global mean temperature, the phase shift of the PDO at the end of the 20th century is suggested to be an influential factor in the recent surface warming hiatus. Therefore, determining the predictability of the PDO in a warming climate is of great importance. By analyzing future climate under different emission scenarios simulated by the Coupled Model Intercomparison Project phase 5 (CMIP5), we show that the prediction lead time and the associated amplitude of the PDO decreases sharply under greenhouse warming conditions. This decrease is largely attributable to a warming-induced intensification of oceanic stratification, which accelerates propagation of Rossby waves, shortening the PDO lifespan and suppressing its amplitude by limiting its growth time. Our results suggest that greenhouse warming will make prediction of the PDO more challenging, with far-reaching ramifications.   </strong></p>

The Spatiotemporal Structure of Twentieth-Century Climate Variations in Observations and Reanalyses. Part I: Long-Term Trend

2008 ◽  
Vol 21 (11) ◽  
pp. 2611-2633 ◽  
Author(s):  
Junye Chen ◽  
Anthony D. Del Genio ◽  
Barbara E. Carlson ◽  
Michael G. Bosilovich
Keyword(s):  
Twentieth Century ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Walker Circulation ◽  
Warming Trend ◽  
Pacific Basin ◽  
Climate Variations ◽  
The Pacific ◽  
Climate Parameter

Abstract The dominant interannual El Niño–Southern Oscillation (ENSO) phenomenon and the short length of climate observation records make it difficult to study long-term climate variations in the spatiotemporal domain. Based on the fact that the ENSO signal spreads to remote regions and induces delayed climate variation through atmospheric teleconnections, an ENSO-removal method is developed through which the ENSO signal can be approximately removed at the grid box level from the spatiotemporal field of a climate parameter. After this signal is removed, long-term climate variations are isolated at mid- and low latitudes in the climate parameter fields from observed and reanalysis datasets. This paper addresses the long-term global warming trend (GW); a companion paper concentrates on Pacific pan-decadal variability (PDV). The warming that occurs in the Pacific basin (approximately 0.4 K in the twentieth century) is much weaker than in surrounding regions and the other two ocean basins (approximately 0.8 K). The modest warming in the Pacific basin is likely due to its dynamic nature on the interannual and decadal time scales and/or the leakage of upper ocean water through the Indonesian Throughflow. Based on the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) and the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), a comprehensive atmospheric structure associated with the GW trend is given. Significant discrepancies exist between the two datasets, especially in the tightly coupled dynamics and water vapor fields. The dynamics fields based on NCEP–NCAR, which show a change in the Walker Circulation, are consistent with the GW change in the surface temperature field. However, intensification in the Hadley Circulation is associated with GW trend in ERA-40 instead.

scholarly journals Is global warming already changing ocean productivity?

2009 ◽  
Vol 6 (6) ◽  
pp. 10311-10354 ◽  
Author(s):  
S. A. Henson ◽  
J. L. Sarmiento ◽  
J. P. Dunne ◽  
L. Bopp ◽  
I. Lima ◽  
...  
Keyword(s):  
Climate Change ◽  
Time Series ◽  
Global Warming ◽  
Primary Production ◽  
Decadal Variability ◽  
Warming Trend ◽  
Natural Variability ◽  
Biogeochemical Models ◽  
Ocean Productivity ◽  
The Impact

Abstract. Global warming is predicted to alter the ocean's biological productivity. But how will we recognise the impacts of climate change on ocean productivity? The most comprehensive information available on the global distribution of ocean productivity comes from satellite ocean colour data. Now that over ten years of SeaWiFS data have accumulated, can we begin to detect and attribute global warming trends in productivity? Here we compare recent trends in SeaWiFS data to longer-term records from three biogeochemical models (GFDL, IPSL and NCAR). We find that detection of real trends in the satellite data is confounded by the relatively short time series and large interannual and decadal variability in productivity. Thus, recent observed changes in chlorophyll, primary production and the size of the oligotrophic gyres cannot be unequivocally attributed to the impact of global warming. Instead, our analyses suggest that a time series of ~40 yr length is needed to distinguish a global warming trend from natural variability. Analysis of modelled chlorophyll and primary production from 2001–2100 suggests that, on average, the global warming trend will not be unambiguously separable from decadal variability until ~2055. Because the magnitude of natural variability in chlorophyll and primary production is larger than, or similar to, the global warming trend, a consistent, decades-long data record must be established if the impact of climate change on ocean productivity is to be definitively detected.

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