scholarly journals Paleo calendar-effect adjustments in time-slice and transient climate-model simulations (PaleoCalAdjust v1.0): impact and strategies for data analysis

2019 ◽  
Vol 12 (9) ◽  
pp. 3889-3913 ◽  
Author(s):  
Patrick J. Bartlein ◽  
Sarah L. Shafer
Keyword(s):  
Climate Model ◽  
Fixed Number ◽  
Time Slice ◽  
Fixed Length ◽  
Daily Data ◽  
Individual Time Series ◽  
Climate Model Output ◽  
Climate Model Simulations ◽  
Definition Of ◽  
The Impact

Abstract. The “paleo calendar effect” is a common expression for the impact that changes in the length of months or seasons over time, related to changes in the eccentricity of Earth's orbit and precession, have on the analysis or summarization of climate-model output. This effect can have significant implications for paleoclimate analyses. In particular, using a “fixed-length” definition of months (i.e., defined by a fixed number of days), as opposed to a “fixed-angular” definition (i.e., defined by a fixed number of degrees of the Earth's orbit), leads to comparisons of data from different positions along the Earth's orbit when comparing paleo with modern simulations. This effect can impart characteristic spatial patterns or signals in comparisons of time-slice simulations that otherwise might be interpreted in terms of specific paleoclimatic mechanisms, and we provide examples for 6, 97, 116, and 127 ka. The calendar effect is exacerbated in transient climate simulations in which, in addition to spatial or map-pattern effects, it can influence the apparent timing of extrema in individual time series and the characterization of phase relationships among series. We outline an approach for adjusting paleo simulations that have been summarized using a modern fixed-length definition of months and that can also be used for summarizing and comparing data archived as daily data. We describe the implementation of this approach in a set of Fortran 90 programs and modules (PaleoCalAdjust v1.0).

scholarly journals Paleo calendar-effect adjustments in time-slice and transient climate-model simulations (PaleoCalAdjust v1.0): impact and strategies for data analysis

2018 ◽  
Author(s):  
Patrick J. Bartlein ◽  
Sarah L. Shafer
Keyword(s):  
Climate Model ◽  
Fixed Number ◽  
Time Slice ◽  
Fixed Length ◽  
Daily Data ◽  
Individual Time Series ◽  
Climate Model Output ◽  
Climate Model Simulations ◽  
Definition Of ◽  
The Impact

Abstract. The “paleo calendar effect” is a common expression for the impact that the changes in the length of months or seasons over time, related to changes in the eccentricity of Earth's orbit and precession, have on the analysis or summarization of climate-model output. This effect can have significant implications for paleoclimate analyses. In particular, using a “fixed-length” definition of months (i.e. defined by a fixed number of days), as opposed to a “fixed-angular” definition (i.e. defined by a fixed number of degrees of the Earth's orbit), leads to comparisons of data from different positions along the Earth's orbit when comparing paleo with modern simulations. This effect can impart characteristic spatial patterns or signals in comparisons of time-slice simulations that otherwise might be interpreted in terms of specific paleoclimatic mechanisms, and we provide examples for 6, 97, 116, and 127 ka. The calendar effect is exacerbated in transient climate simulations, where, in addition to spatial or map-pattern effects, it can influence the apparent timing of extrema in individual time series and the characterization of phase relationships among series. We outline an approach for adjusting paleo simulations that have been summarized using a modern fixed-length definition of months and that can also be used for summarizing and comparing data archived as daily data. We describe the implementation of this approach in a set of Fortran 90 programs and modules (PaleoCalAdjust v1.0).

Future changes in heatwaves over Africa at the convection-permitting scale

2021 ◽  
Author(s):  
Cathryn Birch ◽  
Lawrence Jackson ◽  
Declan Finney ◽  
John Marsham ◽  
Rachel Stratton ◽  
...  
Keyword(s):  
Climate Model ◽  
Daily Rainfall ◽  
Shortwave Radiation ◽  
Daily Maximum ◽  
Future Change ◽  
Driving Mechanisms ◽  
The Future ◽  
Convective Scale ◽  
Climate Model Simulations ◽  
The Impact

<p>Mean temperatures and their extremes have increased over Africa since the latter half of the 20th century and this trend is projected to continue, with very frequent, intense and often deadly heatwaves likely to occur very regularly over much of Africa by 2100. It is crucial that we understand the scale of the future increases in extremes and the driving mechanisms. We diagnose daily maximum wet bulb temperature heatwaves, which allows for both the impact of temperature and humidity, both critical for human health and survivability. During wet bulb heatwaves, humidity and cloud cover increase, which limits the surface shortwave radiation flux but increases longwave warming. It is found from observations and ERA5 reanalysis that approximately 30% of wet bulb heatwaves over Africa are associated with daily rainfall accumulations of more than 1 mm/day on the first day of the heatwave. The first ever pan-African convection-permitting climate model simulations of present-day and RCP8.5 future climate are utilised to illustrate the projected future change in heatwaves, their drivers and their sensitivity to the representation of convection. Compared to ERA5, the convection-permitting model better represents the frequency and magnitude of present-day wet bulb heatwaves than a version of the model with more traditional parameterised convection. The future change in heatwave frequency, duration and magnitude is also larger in the convective-scale simulation, suggesting CMIP-style models may underestimate the future change in wet bulb heat extremes over Africa. The main reason for the larger future change appears to be the ability of the model to produce larger anomalies relative to its climatology in precipitation, cloud and the surface energy balance.</p>

scholarly journals On the Choice of Ensemble Mean for Estimating the Forced Signal in the Presence of Internal Variability

2018 ◽  
Vol 31 (14) ◽  
pp. 5681-5693 ◽  
Author(s):  
Leela M. Frankcombe ◽  
Matthew H. England ◽  
Jules B. Kajtar ◽  
Michael E. Mann ◽  
Byron A. Steinman
Keyword(s):  
Regional Differences ◽  
Climate Model ◽  
Surface Air Temperature ◽  
Internal Variability ◽  
Single Model ◽  
Sea Level Pressure ◽  
Model Simulations ◽  
Ensemble Mean ◽  
Climate Model Simulations ◽  
The Impact

Abstract In this paper we examine various options for the calculation of the forced signal in climate model simulations, and the impact these choices have on the estimates of internal variability. We find that an ensemble mean of runs from a single climate model [a single model ensemble mean (SMEM)] provides a good estimate of the true forced signal even for models with very few ensemble members. In cases where only a single member is available for a given model, however, the SMEM from other models is in general out-performed by the scaled ensemble mean from all available climate model simulations [the multimodel ensemble mean (MMEM)]. The scaled MMEM may therefore be used as an estimate of the forced signal for observations. The MMEM method, however, leads to increasing errors further into the future, as the different rates of warming in the models causes their trajectories to diverge. We therefore apply the SMEM method to those models with a sufficient number of ensemble members to estimate the change in the amplitude of internal variability under a future forcing scenario. In line with previous results, we find that on average the surface air temperature variability decreases at higher latitudes, particularly over the ocean along the sea ice margins, while variability in precipitation increases on average, particularly at high latitudes. Variability in sea level pressure decreases on average in the Southern Hemisphere, while in the Northern Hemisphere there are regional differences.

scholarly journals Trends in Downward Solar Radiation at the Surface over North America from Climate Model Projections and Implications for Solar Energy

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Gerardo Andres Saenz ◽  
Huei-Ping Huang
Keyword(s):  
United States ◽  
North America ◽  
Solar Radiation ◽  
Solar Energy ◽  
Climate Model ◽  
Global Climate Model ◽  
The United States ◽  
Model Simulations ◽  
Climate Model Simulations ◽  
The Impact

The projected changes in the downward solar radiation at the surface over North America for late 21st century are deduced from global climate model simulations with greenhouse-gas (GHG) forcing. A robust trend is found in winter over the United States, which exhibits a simple pattern of a decrease of sunlight over Northern USA. and an increase of sunlight over Southern USA. This structure was identified in both the seasonal mean and the mean climatology at different times of the day. It is broadly consistent with the known poleward shift of storm tracks in winter in climate model simulations with GHG forcing. The centennial trend of the downward shortwave radiation at the surface in Northern USA. is on the order of 10% of the climatological value for the January monthly mean, and slightly over 10% at the time when it is midday in the United States. This indicates a nonnegligible influence of the GHG forcing on solar energy in the long term. Nevertheless, when dividing the 10% by a century, in the near term, the impact of the GHG forcing is relatively minor such that the estimate of solar power potential using present-day climatology will remain useful in the coming decades.

Evolution of Water Vapor Concentrations and Stratospheric Age of Air in Coupled Chemistry-Climate Model Simulations

2007 ◽  
Vol 64 (3) ◽  
pp. 905-921 ◽  
Author(s):  
John Austin ◽  
John Wilson ◽  
Feng Li ◽  
Holger Vömel
Keyword(s):  
Water Vapor ◽  
Greenhouse Gas ◽  
Climate Model ◽  
Sea Surface ◽  
Time Slice ◽  
Sea Surface Temperatures ◽  
Model Simulations ◽  
Stratospheric Water Vapor ◽  
Surface Temperatures ◽  
Climate Model Simulations

Abstract Stratospheric water vapor concentrations and age of air are investigated in an ensemble of coupled chemistry-climate model simulations covering the period from 1960 to 2005. Observed greenhouse gas concentrations, halogen concentrations, aerosol amounts, and sea surface temperatures are all specified in the model as time-varying fields. The results are compared with two experiments (time-slice runs) with constant forcings for the years 1960 and 2000, in which the sea surface temperatures are set to the same climatological values, aerosol concentrations are fixed at background levels, while greenhouse gas and halogen concentrations are set to the values for the relevant years. The time-slice runs indicate an increase in stratospheric water vapor from 1960 to 2000 due primarily to methane oxidation. The age of air is found to be significantly less in the year 2000 run than the 1960 run. The transient runs from 1960 to 2005 indicate broadly similar results: an increase in water vapor and a decrease in age of air. However, the results do not change gradually. The age of air decreases significantly only after about 1975, corresponding to the period of ozone reduction. The age of air is related to tropical upwelling, which determines the transport of methane into the stratosphere. Oxidation of increased methane from enhanced tropical upwelling results in higher water vapor amounts. In the model simulations, the rate of increase of stratospheric water vapor during the period of enhanced upwelling is up to twice the long-term mean. The concentration of stratospheric water vapor also increases following volcanic eruptions during the simulations.

scholarly journals Estimating design hydrologic extremes in a warming climate: alternatives, uncertainties and the way forward

2021 ◽  
Vol 379 (2195) ◽  
pp. 20190623 ◽  
Author(s):  
Ashish Sharma ◽  
Suresh Hettiarachchi ◽  
Conrad Wasko
Keyword(s):  
Climate Model ◽  
Flash Flood ◽  
Design Guidelines ◽  
Design Flood ◽  
The Future ◽  
Flood Magnitude ◽  
Urban Catchments ◽  
Climate Model Simulations ◽  
Hydrologic Design ◽  
The Impact

It is now well established that our warming planet is experiencing changes in extreme storms and floods, resulting in a need to better specify hydrologic design guidelines that can be projected into the future. This paper attempts to summarize the nature of changes occurring and the impact they are having on the design flood magnitude, with a focus on the urban catchments that we will increasingly reside in as time goes on. Two lines of reasoning are used to assess and model changes in design hydrology. The first of these involves using observed storms and soil moisture conditions and projecting how these may change into the future. The second involves using climate model simulations of the future and using them as inputs into hydrologic models to assess the changed design estimates. We discuss here the limitations in both and suggest that the two are, in fact, linked, as climate model projections for the future are needed in the first approach to form meaningful projections for the future. Based on the author's experience with both lines of reasoning, this invited commentary presents a theoretical narrative linking these two and identifying factors and assumptions that need to be validated before implementation in practice. This article is part of a discussion meeting issue ‘Intensification of short-duration rainfall extremes and implications for flash flood risks’.

scholarly journals Decline in Terrestrial Moisture Sources of the Mississippi River Basin in a Future Climate

2020 ◽  
Vol 21 (2) ◽  
pp. 299-316 ◽  
Author(s):  
Imme Benedict ◽  
Chiel C. van Heerwaarden ◽  
Ruud J. van der Ent ◽  
Albrecht H. Weerts ◽  
Wilco Hazeleger
Keyword(s):  
River Basin ◽  
Mississippi River ◽  
Climate Model ◽  
Low Frequency ◽  
Future Climate ◽  
Mississippi River Basin ◽  
Moisture Source ◽  
Moisture Sources ◽  
Climate Model Simulations ◽  
The Impact

AbstractAssessment of the impact of climate change on water resources over land requires knowledge on the origin of the precipitation and changes therein toward the future. We determine the origin of precipitation over the Mississippi River basin (MRB) using high-resolution (~25 km) climate model simulations for present and future climate (RCP4.5). Moisture resulting in precipitation over the MRB is tracked back in time using Eulerian offline moisture tracking, in order to find out from where this water originally evaporated (i.e., the moisture sources). We find that the most important continental moisture sources are the MRB itself and the area southwest of the basin. The two most relevant oceanic sources are the Gulf of Mexico/Caribbean and the Pacific. The distribution of sources varies per season, with more recycling of moisture within the basin during summer and more transport of moisture from the ocean toward the basin in winter. In future winters, we find an increase in moisture source from the oceans (related to higher sea surface temperatures), resulting in more precipitation over the MRB. In future summers, we find an approximately 5% decrease in moisture source from the basin itself, while the decrease in precipitation is smaller (i.e., lower recycling ratios). The results here are based on one climate model, and we do not study low-frequency climate variability. We conclude that Mississippi’s moisture sources will become less local in a future climate, with more water originating from the oceans.

scholarly journals Estimating Changes in Global Temperature since the Preindustrial Period

2017 ◽  
Vol 98 (9) ◽  
pp. 1841-1856 ◽  
Author(s):  
Ed Hawkins ◽  
Pablo Ortega ◽  
Emma Suckling ◽  
Andrew Schurer ◽  
Gabi Hegerl ◽  
...  
Keyword(s):  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Global Temperature ◽  
Radiative Forcings ◽  
Global Average ◽  
Average Temperature ◽  
Climate Model Simulations ◽  
Temperature Levels ◽  
Definition Of

Abstract The United Nations Framework Convention on Climate Change (UNFCCC) process agreed in Paris to limit global surface temperature rise to “well below 2°C above pre-industrial levels.” But what period is preindustrial? Somewhat remarkably, this is not defined within the UNFCCC’s many agreements and protocols. Nor is it defined in the IPCC’s Fifth Assessment Report (AR5) in the evaluation of when particular temperature levels might be reached because no robust definition of the period exists. Here we discuss the important factors to consider when defining a preindustrial period, based on estimates of historical radiative forcings and the availability of climate observations. There is no perfect period, but we suggest that 1720–1800 is the most suitable choice when discussing global temperature limits. We then estimate the change in global average temperature since preindustrial using a range of approaches based on observations, radiative forcings, global climate model simulations, and proxy evidence. Our assessment is that this preindustrial period was likely 0.55°–0.80°C cooler than 1986–2005 and that 2015 was likely the first year in which global average temperature was more than 1°C above preindustrial levels. We provide some recommendations for how this assessment might be improved in the future and suggest that reframing temperature limits with a modern baseline would be inherently less uncertain and more policy relevant.

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