On the persistence of near-surface temperature dynamics in a warming world.

We consider issues related to the effect of climate change on the persistence of (trend-corrected) temperatures using global gridded data for both land and oceans. We first discuss how the presence of trends and additive noise affects inference about persistence. Ignoring a trend induces an upward bias, while not accounting for noise induces a downward bias. We show that the increase in persistence in the commonly used Warm Spell Duration Index is simply an artifact of increasing temperatures. To purge the impact of both trends and noise, we adopt a simple state-space model. Of separate interest, we document a much larger noise component for land than for oceans. The estimates of the persistence are much larger for oceans than for land. Inspection of the estimates across various subsamples and the application of tests for structural changes suggest the same pattern of persistence for both land and oceans across time, with few minor exceptions. Hence, our results show that surface temperature persistence has remained constant during the observed period.

The Effect of Exercise Modalities on Walking Capacity in Patients With Intermittent Claudication: A NETWORK META-ANALYSIS.

INTRODUCTION: Despite extensive research on the effect of supervised exercise therapy on walking performance in patients with symptomatic peripheral arterial disease (PAD), it remains unclear which training modality provides the greatest improvement in walking capacity. The objective of this study was to compare the effect of different types of supervised exercise therapy on walking capacity in individuals with symptomatic PAD. METHODS: A random-effect network meta-analysis was performed. The following databases were searched from January 1966 to April 2021: SPORTDiscus, CINAHL, MEDLINE, AMED, Academic Search Complete and, Scopus. Trials had to include at least one type of supervised exercise therapy for patients with symptomatic PAD, with an intervention lasting ≥2 wk with ≥5 training sessions, and an objective measure of walking capacity. RESULTS: Eighteen studies were included for a total sample of 1135 participants. Interventions duration ranged from 6-24 wk and included aerobic exercise (treadmill walking, ergometer, and Nordic walking), resistance training (lower and/or upper body), a combination of both, and underwater exercise. Results showed that combined training improved treadmill walking capacity to a comparable extent to aerobic walking (+122.0 [24.2-219.8] m vs +106.8 [34.2-179.4] m), but with a larger effect size (1.20 [0.50-1.90] vs 0.67 [0.22-1.11]). Similar results were observed for the 6-min walk distance, with combined training being the most promising modality (+57.3 [16.2-98.5] m), followed by underwater training (+56.5 [22.4-90.5] m) and aerobic walking (+39.0 [12.8-65.1] m). CONCLUSION: While not statistically superior to aerobic walking, combined exercise seems to be the most promising training modality. Aerobic walking and underwater training also improved walking capacity for patients with symptomatic PAD.

Anthropogenic influence on extremes and risk hotspots.

Study of the frequency and magnitude of climate extremes as the world warms is of utmost importance, especially separating the influence of natural and anthropogenic forcing factors. Record-breaking temperature and precipitation events have been studied using event-attribution techniques. Here, we provide spatial and temporal observation-based analyses of the role of natural and anthropogenic factors, using state-of-the-art time series methods. We show that the risk from extreme temperature and rainfall events has severely increased for most regions worldwide. In some areas the probabilities of occurrence of extreme temperatures and precipitation have increased at least fivefold and twofold, respectively. Anthropogenic forcing has been the main driver of such increases and its effects amplify those of natural forcing. We also identify risk hotspots defined as regions for which increased risk of extreme events and high exposure in terms of either high Gross Domestic Product (GDP) or large population are both present. For the year 2018, increased anthropogenic forcings are mostly responsible for increased risk to extreme temperature/precipitation affecting 94%/72% of global population and 97%/76% of global GDP relative to the baseline period 1961-1990.

Disentangling the trend in the warming of urban areas into global and local factors.

Large cities account for a significant share of national population and wealth, and exert high pressure on local and regional resources, exacerbating socioenvironmental risks. The replacement of natural landscapes with higher heat capacity materials because of urbanization and anthropogenic waste heat are some of the factors contributing to local climate change caused by the urban heat island (UHI) effect. Because of synergistic effects, local climate change can exacerbate the impacts of global warming in cities. Disentangling the contributions to warming in cities from global and local drivers can help to understand their relative importance and guide local adaptation policies. The canopy UHI intensity is commonly approximated by the difference between temperatures within cities and the surrounding areas. We present a complementary approach that applies the concept of common trends to extract the global contributions to observed warming in cities and to obtain a residual warming trend caused by local and regional factors. Once the effects of global drivers are removed, common features appear in cities' temperatures in the eastern part of the United States. Most cities experienced higher warming than that attributable to global climate change, and some shared a period of rapid warming during urban sprawl in the mid-20th century in the United States.

Spatial variations in the warming trend and the transition to more severe weather in midlatitudes.

Due to various feedback processes called Arctic amplification, the high-latitudes' response to increases in radiative forcing is much larger than elsewhere in the world, with a warming more than twice the global average. Since the 1990's, this rapid warming of the Arctic was accompanied by no-warming or cooling over midlatitudes in the Northern Hemisphere in winter (the hiatus). The decrease in the thermal contrast between Arctic and midlatitudes has been connected to extreme weather events in midlatitudes via, e.g., shifts in the jet stream towards the equator and increases in the probability of high-latitude atmospheric blocking. Here we present an observational attribution study showing the spatial structure of the response to changes in radiative forcing. The results also connect the hiatus with diminished contrast between temperatures over regions in the Arctic and midlatitudes. Recent changes in these regional warming trends are linked to international actions such as the Montreal Protocol, and illustrate how changes in radiative forcing can trigger unexpected responses from the climate system. The lesson for climate policy is that human intervention with the climate is already large enough that even if stabilization was attained, impacts from an adjusting climate are to be expected.

Causality from long-lived radiative forcings to the climate trend.

In our study, we present a purely statistical observations-based model-free analysis that provides evidence about Granger causality (GC) from long-lived radiative forcings (LLRFs) to the climate trend (CT). This relies on having locally ordered breaks in the slopes of the trend functions of LLRF and the CT, with the break for LLRF occurring before that of the CT and with the slope changes being of the same sign. The empirical evidence indicates that these conditions are satisfied empirically using standard global surface temperature series and an aggregate measure of LLRF (carbon dioxide, nitrous oxide, and chlorofluorocarbons). We also discuss why the presence of broken trends can lead one to conclude in favor of GC when using standard methods even if the noise function in LLRF is negligible.

A time-series analysis of the 20th century climate simulations produced for the IPCC's Fourth Assessment Report.

In this paper evidence of anthropogenic influence over the warming of the 20th century is presented and the debate regarding the time-series properties of global temperatures is addressed in depth. The 20th century global temperature simulations produced for the Intergovernmental Panel on Climate Change's Fourth Assessment Report and a set of the radiative forcing series used to drive them are analyzed using modern econometric techniques. Results show that both temperatures and radiative forcing series share similar time-series properties and a common nonlinear secular movement. This long-term co-movement is characterized by the existence of time-ordered breaks in the slope of their trend functions. The evidence presented in this paper suggests that while natural forcing factors may help explain the warming of the first part of the century, anthropogenic forcing has been its main driver since the 1970's. In terms of Article 2 of the United Nations Framework Convention on Climate Change, significant anthropogenic interference with the climate system has already occurred and the current climate models are capable of accurately simulating the response of the climate system, even if it consists in a rapid or abrupt change, to changes in external forcing factors. This paper presents a new methodological approach for conducting time-series based attribution studies.