Historical Reconstruction of Anthropogenic Carbon and Excess Heat Content in the Subtropical North Atlantic Ocean

2020 ◽  
Author(s):  
Herle Mercier ◽  
Marie-Jose Messias
Keyword(s):  
Global Warming ◽  
Radiative Forcing ◽  
Hot Spot ◽  
Ocean Dynamics ◽  
Strong Increase ◽  
Historical Reconstruction ◽  
Continuous Increase ◽  
Excess Heat ◽  
Source Regions ◽  
Anthropogenic Carbon

<p>The oceans have mitigated global warming by the absorption of 90% of the excess heat resulting from anthropogenic radiative forcing and of 1/3 of the anthropogenic carbon (Cant). There are still major uncertainties concerning their regional rates of uptake (or loss), transport and storage by the oceans, knowledge of which is key to the heat and carbon balances, and essential to reduce the uncertainties in global warming prediction. Here, we used tracers observations (transient and passive CFC-11, CFC-12, SF<sub>6</sub>, natural C14, the conservative PO<sub>4</sub>* and NO<sub>3</sub>*, salinity and temperature) and a maximum entropy inverse method to compute Green’s functions (G), which contain intrinsically information on ocean dynamics and transit times from the source regions. From G, we propagated surface history of temperature and Cant to reconstruct their fields in the ocean for the industrial era and to quantify their source regions. We present reconstructions of Cant and excess heat (taken as the temperature anomaly from 1850) along the 24°N trans-Atlantic section, at the crossroads of the main contributors of the AMOC and an hot spot of heat and carbon storage, from 5 repeats spanning 1992 to 2015. We show that Cant reconstructions, dominated by the strong increase of Cant in the atmosphere, compare well with a previous global historical reconstruction as well as Cant estimates in the water masses at 24°N. The excess heat reconstructions are tempered by the natural variability that can exceed the anthropogenic trend. They show a net invasion and warming of the top 800m from the 1920’s (0.01°C/y). The trend slightly weakens in the late 1970’s followed by an acceleration from the 2000’s (0.02°C/y). For the well–ventilated deeper waters of the DWBC around 1500m, after a notable cooling period, a weak warming departs in the 1950’s with a trend of 0.001°C/y up to the 2000’s and of 0.006°C/y afterwards. The waters below 2000m suggest a continuous warming from the 1930’s, with a more pronounced trend centered at 3000m of 0.001°C/y up to the 2000’s and of 0.003°C/y afterwards. This excess heat evolution in the DWBC contrasts with the Cant evolution which shows continuous increase in Cant content in the upper NADW. Our results highlight the difference of drowning up of Cant ant heat into the deeper ocean, reflecting their different surface histories in the formation regions.</p>

scholarly journals Effects of climate change on spatiotemporal patterns of tropical cyclone tracks and their implications for coastal agriculture in Myanmar

2021 ◽  
Author(s):  
Akira Hirano
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
Considerable Increase ◽  
Hot Spot ◽  
Coastal Region ◽  
Storm Surges ◽  
Coastal Areas ◽  
Spatiotemporal Patterns ◽  
Sea Levels ◽  
Rising Sea Levels

AbstractImportant aspects for understanding the effects of climate change on tropical cyclones (TCs) are the frequency of TCs and their tracking patterns. Coastal areas are increasingly threatened by rising sea levels and associated storm surges brought on by TCs. Rice production in Myanmar relies strongly on low-lying coastal areas. This study aims to provide insights into the effects of global warming on TCs and the implications for sustainable development in vulnerable coastal areas in Myanmar. Using TC records from the International Best Track Archive for Climate Stewardship dataset during the 30-year period from 1983 to 2012, a hot spot analysis based on Getis-Ord (Gi*) statistics was conducted to identify the spatiotemporal patterns of TC tracks along the coast of Myanmar. The results revealed notable changes in some areas along the central to southern coasts during the study period. These included a considerable increase in TC tracks (p value < 0.01) near the Ayeyarwady Delta coast, otherwise known as “the rice bowl” of the nation. This finding aligns with trends in published studies and reinforced the observed trends with spatial statistics. With the intensification of TCs due to global warming, such a significant increase in TC experiences near the major rice-producing coastal region raises concerns about future agricultural sustainability.

scholarly journals A Link between the Hiatus in Global Warming and North American Drought

2015 ◽  
Vol 28 (9) ◽  
pp. 3834-3845 ◽  
Author(s):  
Thomas L. Delworth ◽  
Fanrong Zeng ◽  
Anthony Rosati ◽  
Gabriel A. Vecchi ◽  
Andrew T. Wittenberg
Keyword(s):  
Global Warming ◽  
North America ◽  
Surface Temperature ◽  
North American ◽  
Radiative Forcing ◽  
Tropical Pacific ◽  
Global Warming Hiatus ◽  
Warming Hiatus ◽  
The Impact ◽  
The Tropical Pacific

Abstract Portions of western North America have experienced prolonged drought over the last decade. This drought has occurred at the same time as the global warming hiatus—a decadal period with little increase in global mean surface temperature. Climate models and observational analyses are used to clarify the dual role of recent tropical Pacific changes in driving both the global warming hiatus and North American drought. When observed tropical Pacific wind stress anomalies are inserted into coupled models, the simulations produce persistent negative sea surface temperature anomalies in the eastern tropical Pacific, a hiatus in global warming, and drought over North America driven by SST-induced atmospheric circulation anomalies. In the simulations herein the tropical wind anomalies account for 92% of the simulated North American drought during the recent decade, with 8% from anthropogenic radiative forcing changes. This suggests that anthropogenic radiative forcing is not the dominant driver of the current drought, unless the wind changes themselves are driven by anthropogenic radiative forcing. The anomalous tropical winds could also originate from coupled interactions in the tropical Pacific or from forcing outside the tropical Pacific. The model experiments suggest that if the tropical winds were to return to climatological conditions, then the recent tendency toward North American drought would diminish. Alternatively, if the anomalous tropical winds were to persist, then the impact on North American drought would continue; however, the impact of the enhanced Pacific easterlies on global temperature diminishes after a decade or two due to a surface reemergence of warmer water that was initially subducted into the ocean interior.

Extreme North America Winter Storm Season of 2013/14: Roles of Radiative Forcing and the Global Warming Hiatus

2015 ◽  
Vol 96 (12) ◽  
pp. S25-S28 ◽  
Author(s):  
Xiaosong Yang ◽  
G. A. Vecchi ◽  
T. L. Delworth ◽  
K. Paffendorf ◽  
L. Jia ◽  
...  
Keyword(s):  
Global Warming ◽  
North America ◽  
Radiative Forcing ◽  
Winter Storm ◽  
Global Warming Hiatus ◽  
Warming Hiatus ◽  
Extreme North

scholarly journals Atmospheric Lifetimes, Infrared Absorption Spectra, Radiative Forcings and Global Warming Potentials of NF<sub>3</sub> and CFC-115

2016 ◽  
Author(s):  
Anna Totterdill ◽  
Tamás Kovács ◽  
Wuhu Feng ◽  
Sandip Dhomse ◽  
Christopher J. Smith ◽  
...  
Keyword(s):  
Global Warming ◽  
Cross Sections ◽  
Infrared Absorption ◽  
Radiative Forcing ◽  
Climate Model ◽  
Radiative Forcings ◽  
Atmospheric Window ◽  
Infrared Absorption Spectra ◽  
Global Warming Potentials ◽  
Good Agreement

Abstract. Fluorinated compounds such as NF3 and C2F5Cl (CFC-115) are characterised by very large global warming potentials (GWPs) which result from extremely long atmospheric lifetimes and strong infrared absorptions in the atmospheric window. In this study we have experimentally determined the infrared absorption cross-sections of NF3 and CFC-115, calculated the radiative forcing and efficiency using two radiative transfer models and identified the effect of clouds and stratospheric adjustment. The infrared cross sections are in good agreement with previous measurements, whereas the resulting radiative forcings and efficiencies are, on average, around 10 % larger. A whole atmosphere chemistry-climate model was used to determine the atmospheric lifetimes of NF3 and CFC-115 to be (616 ± 34) years and (492 ± 22) years, respectively. The GWPs for NF3 are estimated to be 14 600, 19 400 and 21 400 over 20, 100 and 500 years, respectively. Similarly, the GWPs for CFC-115 are 6120, 8060 and 8630 over 20, 100 and 500 years, respectively.

scholarly journals Last Glacial Maximum (LGM) climate forcing and ocean dynamical feedback and their implications for estimating climate sensitivity

2021 ◽  
Vol 17 (1) ◽  
pp. 253-267
Author(s):  
Jiang Zhu ◽  
Christopher J. Poulsen
Keyword(s):  
Last Glacial Maximum ◽  
Ocean Circulation ◽  
Climate Sensitivity ◽  
Radiative Forcing ◽  
Ice Sheets ◽  
Glacial Maximum ◽  
Ocean Dynamics ◽  
Last Glacial ◽  
True Value ◽  
Climate Forcings

Abstract. Equilibrium climate sensitivity (ECS) has been directly estimated using reconstructions of past climates that are different than today's. A challenge to this approach is that temperature proxies integrate over the timescales of the fast feedback processes (e.g., changes in water vapor, snow, and clouds) that are captured in ECS as well as the slower feedback processes (e.g., changes in ice sheets and ocean circulation) that are not. A way around this issue is to treat the slow feedbacks as climate forcings and independently account for their impact on global temperature. Here we conduct a suite of Last Glacial Maximum (LGM) simulations using the Community Earth System Model version 1.2 (CESM1.2) to quantify the forcing and efficacy of land ice sheets (LISs) and greenhouse gases (GHGs) in order to estimate ECS. Our forcing and efficacy quantification adopts the effective radiative forcing (ERF) and adjustment framework and provides a complete accounting for the radiative, topographic, and dynamical impacts of LIS on surface temperatures. ERF and efficacy of LGM LIS are −3.2 W m−2 and 1.1, respectively. The larger-than-unity efficacy is caused by the temperature changes over land and the Northern Hemisphere subtropical oceans which are relatively larger than those in response to a doubling of atmospheric CO2. The subtropical sea-surface temperature (SST) response is linked to LIS-induced wind changes and feedbacks in ocean–atmosphere coupling and clouds. ERF and efficacy of LGM GHG are −2.8 W m−2 and 0.9, respectively. The lower efficacy is primarily attributed to a smaller cloud feedback at colder temperatures. Our simulations further demonstrate that the direct ECS calculation using the forcing, efficacy, and temperature response in CESM1.2 overestimates the true value in the model by approximately 25 % due to the neglect of slow ocean dynamical feedback. This is supported by the greater cooling (6.8 ∘C) in a fully coupled LGM simulation than that (5.3 ∘C) in a slab ocean model simulation with ocean dynamics disabled. The majority (67 %) of the ocean dynamical feedback is attributed to dynamical changes in the Southern Ocean, where interactions between upper-ocean stratification, heat transport, and sea-ice cover are found to amplify the LGM cooling. Our study demonstrates the value of climate models in the quantification of climate forcings and the ocean dynamical feedback, which is necessary for an accurate direct ECS estimation.

scholarly journals The relationship between net GHG emissions and radiative forcing with an application to Article 4.1 of the Paris Agreement.

2021 ◽  
Author(s):  
Tom M. L. Wigley
Keyword(s):  
Global Warming ◽  
Radiative Forcing ◽  
Ghg Emissions ◽  
Zero Point ◽  
Paris Agreement ◽  
Test Case ◽  
Net Zero ◽  
Global Warming Potentials ◽  
The Relationship

Abstract This paper provides an assessment of Article 4.1 of the Paris Agreement on climate; the main goal of which is to provide guidance on how “to achieve the long-term temperature goal set out in Article 2”. Paraphrasing, Article 4.1 says that, to achieve this end, we should decrease greenhouse gas (GHG) emissions so that net anthropogenic GHG emissions fall to zero in the second half of this century. To aggregate net GHG emissions, 100-year Global Warming Potentials (GWP-100) are commonly used to convert non-CO2 emissions to equivalent CO2 emissions. As a test case using methane, temperature projections using GWP-100 scaling are shown to be seriously in error. This throws doubt on the use of GWP-100 scaling to estimate net GHG emissions. An alternative method to determine the net-zero point for GHG emissions based on radiative forcing is derived. This shows that the net-zero point needs to be reached as early as 2036, much sooner than in the Article 4.1 window. Other scientific flaws in Article 4.1 that further undermine its purpose to guide efforts to achieve the Article 2 temperature targets are discussed.

scholarly journals Total aerosol effect: radiative forcing or radiative flux perturbation?

2009 ◽  
Vol 9 (6) ◽  
pp. 25633-25661 ◽  
Author(s):  
U. Lohmann ◽  
L. Rotstayn ◽  
T. Storelvmo ◽  
A. Jones ◽  
S. Menon ◽  
...  
Keyword(s):  
Global Warming ◽  
Radiative Forcing ◽  
Climate Models ◽  
Radiative Flux ◽  
Radiative Forcings ◽  
Microphysical Properties ◽  
Aerosol Effect ◽  
Rain Formation ◽  
Aerosol Radiative ◽  
Flux Perturbation

Abstract. Uncertainties in aerosol radiative forcings, especially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation introduces feedbacks which can affect the rate of rain formation. In former assessments of aerosol radiative forcings, these effects have not been quantified. Also, with global aerosol-climate models simulating interactively aerosols and cloud microphysical properties, a quantification of the aerosol forcings in the traditional way is difficult to properly define. Here we argue that fast feedbacks should be included because they act quickly compared with the time scale of global warming. We show that for different forcing agents (aerosols and greenhouse gases) the radiative forcings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturbations (RFP), that takes these fast feedbacks and interactions into account. Based on our results, we recommend RFP as a valid option to compare different forcing agents, and to compare the effects of particular forcing agents in different models.

scholarly journals Competing Influences of Anthropogenic Warming, ENSO, and Plant Physiology on Future Terrestrial Aridity

2017 ◽  
Vol 30 (17) ◽  
pp. 6883-6904 ◽  
Author(s):  
Céline Bonfils ◽  
Gemma Anderson ◽  
Benjamin D. Santer ◽  
Thomas J. Phillips ◽  
Karl E. Taylor ◽  
...  
Keyword(s):  
Global Warming ◽  
Radiative Forcing ◽  
Potential Evapotranspiration ◽  
Southern Oscillation ◽  
Stomatal Resistance ◽  
Ocean Warming ◽  
Evaporative Demand ◽  
Enso Variability ◽  
Soil Desiccation ◽  
Plant Water Use

The 2011–16 California drought illustrates that drought-prone areas do not always experience relief once a favorable phase of El Niño–Southern Oscillation (ENSO) returns. In the twenty-first century, such an expectation is unrealistic in regions where global warming induces an increase in terrestrial aridity larger than the changes in aridity driven by ENSO variability. This premise is also flawed in areas where precipitation supply cannot offset the global warming–induced increase in evaporative demand. Here, atmosphere-only experiments are analyzed to identify land regions where aridity is currently sensitive to ENSO and where projected future changes in mean aridity exceed the range caused by ENSO variability. Insights into the drivers of these changes in aridity are obtained using simulations with the incremental addition of three different factors to the current climate: ocean warming, vegetation response to elevated CO2levels, and intensified CO2radiative forcing. The effect of ocean warming overwhelms the range of ENSO-driven temperature variability worldwide, increasing potential evapotranspiration (PET) in most ENSO-sensitive regions. Additionally, about 39% of the regions currently sensitive to ENSO will likely receive less precipitation in the future, independent of the ENSO phase. Consequently aridity increases in 67%–72% of the ENSO-sensitive area. When both radiative and physiological effects are considered, the area affected by arid conditions rises to 75%–79% when using PET-derived measures of aridity, but declines to 41% when an aridity indicator for total soil moisture is employed. This reduction mainly occurs because plant stomatal resistance increases under enhanced CO2concentrations, resulting in improved plant water-use efficiency, and hence reduced evapotranspiration and soil desiccation. Imposing CO2-invariant stomatal resistance may overestimate future drying in PET-derived indices.

scholarly journals Concentrations and source regions of light absorbing impurities in snow/ice in northern Pakistan and their impact on snow albedo

2017 ◽  
Author(s):  
Chaman Gul ◽  
Siva Praveen Puppala ◽  
Shichang Kang ◽  
Bhupesh Adhikary ◽  
Yulan Zhang ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Transport Model ◽  
Chemical Transport ◽  
Small Contribution ◽  
Northern Pakistan ◽  
Chemical Transport Model ◽  
Transport Modelling ◽  
Snow Albedo ◽  
Source Regions ◽  
Snow And Ice

Abstract. Black carbon (BC), water-insoluble organic carbon (OC), and mineral dust are important particulate impurities in snow and ice, which significantly reduce albedo and accelerate melting. Surface snow and ice samples were collected from the Karakoram–Himalayan region of northern Pakistan during 2015 and 2016 in summer (six glaciers), autumn (two glaciers), and winter (six mountain valleys). The average BC concentration overall was 2130 ± 1560 ngg−1 in summer samples, 2883 ± 3439 ngg−1 in autumn samples, and 992 ± 883 ngg−1 in winter samples. The average water insoluble OC concentration overall was 1839 ± 1108 ngg−1 in summer samples, 1423 ± 208 ngg−1 in autumn samples, and 1342 ± 672 ngg−1 in winter samples. The overall concentration of BC, OC, and dust in aged snow samples collected during the summer campaign was higher than the concentration in ice samples. The values are relatively high compared to reports by others for the Himalayas and Tibetan Plateau. This is probably the result of taking more representative samples at lower elevation where deposition is higher and the effects of ageing and enrichment more marked. A reduction in snow albedo of 0.1–8.3 % for fresh snow and 0.9–32.5 % for aged snow was calculated for selected solar zenith angles during day time using the Snow, Ice, and Aerosol Radiation (SNICAR) model. Daily mean albedo was reduced by 0.07–12.0 %. The calculated radiative forcing ranged from 0.16 to 43.45 Wm−2 depending on snow type, solar zenith angle, and location. The potential source regions of the deposited pollutants were identified using spatial variance in wind vector maps, emission inventories coupled with backward air trajectories, and simple region tagged chemical transport modelling. Central, South, and West Asia were the major sources of pollutants during the sampling months, with only a small contribution from East Asia. Analysis based on the Weather Research and Forecasting (WRF-STEM) chemical transport model identified a significant contribution (more than 70 %) from South Asia at selected sites. Research into the presence and effect of pollutants in the glaciated areas of Pakistan is economically significant because the surface water resources in the country mainly depend on the rivers (the Indus and its tributaries) that flow from this glaciated area.

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