Report Postclose
Remove Postclose
Are you sure? After you remove the post, it will no longer appear in channel listings but you can access it directly. You can undo this later by clicking "approve".
Delete Postclose
Are you sure you want to delete this post? This is a permanent action and cannot be reversed.
What caused the global warming 1930-1940? Sea level rose during this period at a rate equal to today
Fingerprints of internal drivers of Arctic sea ice loss in observations and model simulations
Nature Geoscience volume 12, pages 28–33 (2019)Cite this article [Qinghua Ding](javascript:;), Axel Schweiger, Michelle L’Heureux, Eric J. Steig, David S. Battisti, Nathaniel C. Johnson, Eduardo Blanchard-Wrigglesworth, Stephen Po-Chedley,Qin Zhang, Kirstin Harnos, Mitchell Bushuk, Bradley Markle & Ian Baxter
Abstract
The relative contribution and physical drivers of internal variability in recent Arctic sea ice loss remain open questions, leaving up for debate whether global climate models used for climate projection lack sufficient sensitivity in the Arctic to climate forcing. Here, through analysis of large ensembles of fully coupled climate model simulations with historical radiative forcing, we present an important internal mechanism arising from low-frequency Arctic atmospheric variability in models that can cause substantial summer sea ice melting in addition to that due to anthropogenic forcing. This simulated internal variability shows a strong similarity to the observed Arctic atmospheric change in the past 37 years. Through a fingerprint pattern matching method, we estimate that this internal variability contributes to about 40–50% of observed multi-decadal decline in Arctic sea ice. Our study also suggests that global climate models may not actually underestimate sea ice sensitivities in the Arctic, but have trouble fully replicating an observed linkage between the Arctic and lower latitudes in recent decades. Further improvements in simulating the observed Arctic–global linkage are thus necessary before the Arctic’s sensitivity to global warming in models can be quantified with confidence.
Number of page(s)
10
Section
The Sun
DOI
https://doi.org/10.1051/0004-6361/201731199
Published online
18 July 2018
A&A 615, A85 (2018)
Revised historical solar irradiance forcing
T. Egorova1, W. Schmutz1, E. Rozanov1,2, A. I. Shapiro3, I. Usoskin4, J. Beer5, R. V. Tagirov6 and T. Peter2
Received: 18 May 2017 Accepted: 11 March 2018
Abstract
Context. There is no consensus on the amplitude of historical solar forcing. The estimated magnitude of the total solar irradiance (TSI) difference between the Maunder minimum and the present time ranges from 0.1 to 6 W m−2 making the simulation of the past and future climate uncertain. One reason for this disagreement is the applied evolution of the quiet Sun brightness in solar irradiance reconstruction models. This work addresses the role of the quiet Sun model choice and updated solar magnetic activity proxies on the solar forcing reconstruction.
Aims. We aim to establish a plausible range for the solar irradiance variability on decadal to millennial timescales.
Methods. The spectral solar irradiance (SSI) is calculated as a weighted sum of the contributions from sunspot umbra, sunspot penumbra, faculae, and quiet Sun, which are pre-calculated with the NLTE Spectral SYnthesis code (NESSY). We introduce activity belts of the contributions from sunspots and faculae and a new structure model for the quietest state of the Sun. We assume that the brightness of the quiet Sun varies in time proportionally to the secular (22-yr smoothed) variation of the solar modulation potential.
Results. A new reconstruction of the TSI and SSI covering the period 6000 BCE - 2015 CE is presented. The model simulates solar irradiance variability during the satellite era well. The TSI change between the Maunder and recent minima ranges between 3.7 and 4.5 W m−2 depending on the applied solar modulation potential. The implementation of a new quietest Sun model reduces, by approximately a factor of two, the relative solar forcing compared to the largest previous estimation, while the application of an updated solar modulation potential increases the forcing difference between the Maunder minimum and the present by 25–40%.
· Natureetter
Pacific contribution to the early twentieth-century warming in the Arctic
· Lea Svendsen,
· Ingo Bethke,
· Yongqi Gao &
Nature Climate Change volume 8, pages 793–797 (2018)Cite this article
· 2434 Accesses
· 28 Citations
· 99 Altmetric
Abstract
Arctic surface temperature warmed more than twice as fast as global temperature during the early twentieth century, similar to that during the recent global warming. This Arctic warming has been attributed to both external forcing1 and internal variability associated with atmospheric dynamics2,3 and Atlantic Ocean temperature4 in combination with Pacific variability5. Here we show, through coupled climate model experiments that superpose externally forced and dynamically driven changes, that Pacific decadal variability alone was a key contributor to the early twentieth century Arctic warming. Sea surface temperatures in the model are phased to observations by prescribing historical wind variations over the Pacific, which drive thermodynamically consistent decadal variations. During the early twentieth century, the Pacific Decadal Oscillation (PDO) transitioned to a positive phase with a concomitant deepening of the Aleutian Low that warms the Arctic by poleward low-level advection of extratropical air. In addition, our experiments revealed that the implemented Pacific surface changes weaken the polar vortex, which leads to subsidence-induced adiabatic heating of the Arctic surface. Thus, our results suggest that the observed recent shift to the positive PDO phase6 will intensify Arctic warming in the forthcoming decades. [edited by author]