Early onset of significant local warming in low latitude countries

Abstract

The Earth is warming on average, and most of the global warming of the past half-century can very likely be attributed to human influence. But the climate in particular locations is much more variable, raising the question of where and when local changes could become perceptible enough to be obvious to people in the form of local warming that exceeds interannual variability; indeed only a few studies have addressed the significance of local signals relative to variability. It is well known that the largest total warming is expected to occur in high latitudes, but high latitudes are also subject to the largest variability, delaying the emergence of significant changes there. Here we show that due to the small temperature variability from one year to another, the earliest emergence of significant warming occurs in the summer season in low latitude countries (≈25 • S-25 • N). We also show that a local warming signal that exceeds past variability is emerging at present, or will likely emerge in the next two decades, in many tropical countries. Further, for most countries worldwide, a mean global warming of 1 • C is sufficient for a significant temperature change, which is less than the total warming projected for any economically plausible emission scenario. The most strongly affected countries emit small amounts of CO 2 per capita and have therefore contributed little to the changes in climate that they are beginning to experience.

Pace of shifts in climate regions increases with global temperature

“…Almost all land areas of the northern middle and high latitudes undergo climate shifts, whereas the tropical regions do not see many changes. This seems at first glance to be in contradiction to previous findings where temperature increases show the earliest emerging signals in the tropics 1 . However, as the Köppen classes are threshold based, and tropical climates already have hot summers, a further increase in temperature generally will not affect the climate class.…”

“…Human induced climate change causes significant changes in local climates 1 Using the RCP8.5 emissions pathway, the pace nearly doubles by the end of this century and about 20% of all land area undergoes a change in its original climate. This implies that species will have increasingly less time to adapt to Köppen zone changes in the future, which is expected to increase the risk of extinction 5 .…”

A framework for modeling uncertainty in regional climate change

“…Other sources of uncertainty in future climate projections, in particular at the regional level, include natural variability and structural uncertainty associated with differences in parameterization in existing climate models. It is well known that year-to-year variability in the climate system is large, in particular at high latitudes, making the emergence of significant climate change slow and signal-to-noise detection difficult (Mahlstein et al 2011(Mahlstein et al , 2012Hawkins and Sutton 2012). At the same time, climate projections are heavily influenced by the characteristics of the chosen climate model and global climate models remain inconsistent in capturing regional precipitation changes and other atmospheric processes.…”

Uncertainties in the timing of unprecedented climates

“…El Niño events). These fluctuations occur randomly and independently, in both reality and individual modelbased projections, and act to obscure the climate change signal 3,4,5 . M13 discuss projections of when changes in climate emerge permanently above the levels of such fluctuations (a metric first considered by ref.…”

“…The reason for 'high confidence' is that tropical temperature emergence has already been seen in observations 6,10,11 and in many previous studies examining climate simulations 3,4,6,11,12,13,14,15,16,17,18 , none of which were cited by M13. While projections of emergence times are clearly important for estimating a wide range of impacts (as demonstrated for food security 17 , biodiversity hotspots 18 and ocean biogeochemistry 19 ), they must be quantified within a framework that incorporates climate variability, as illustrated in the large body of literature that has already examined this issue.…”