Changing State of the Climate System

Abstract

Chapter 2 assesses observed large-scale changes in climate system drivers, key climate indicators and principal modes of variability. Chapter 3 considers model performance and detection/attribution, and Chapter 4 covers projections for a subset of these same indicators and modes of variability. Collectively, these chapters provide the basis for later chapters, which focus upon processes and regional changes. Within Chapter 2, changes are assessed from in situ and remotely sensed data and products and from indirect evidence of longer-term changes based upon a diverse range of climate proxies. The timeevolving availability of observations and proxy information dictate the periods that can be assessed. Wherever possible, recent changes are assessed for their significance in a longer-term context, including target proxy periods, both in terms of mean state and rates of change.The increase in GMST since the mid-19th century was preceded by a slow decrease that began in the mid-Holocene (around 6500 years ago) (medium confidence). {2.3.1.1, Cross-Chapter Box 2.1} Changes in GMST and global surface air temperature (GSAT) over time differ by at most 10% in either direction (high confidence), and the long-term changes in GMST and GSAT are presently assessed to be identical. There is expanded uncertainty in GSAT estimates, with the assessed change from 1850-1900 to 1995-2014 being 0.85 [0.67 to 0.98] °C. {Cross-Chapter Box 2.3} The troposphere has warmed since at least the 1950s, and it is virtually certain that the stratosphere has cooled. In the Tropics, the upper troposphere has warmed faster than the near-surface since at least 2001, the period over which new observational techniques permit more robust quantification (medium confidence). It is virtually certain that the tropopause height has risen globally over 1980-2018, but there is low confidence in the magnitude. {2.3.1.2} Changes in several components of the global hydrological cycle provide evidence for overall strengthening since at least 1980 (high confidence). However, there is low confidence in comparing recent changes with past variations due to limitations in paleoclimate records at continental and global scales. Global land precipitation has likely increased since 1950, with a faster increase since the 1980s (medium confidence). Nearsurface specific humidity has increased over both land (very likely) and the oceans (likely) since at least the 1970s. Relative humidity has very likely decreased over land areas since 2000. Global total column water vapour content has very likely increased during the satellite era. Observational uncertainty leads to low confidence in global trends in precipitation minus evaporation and river runoff. {2.3.1.3} Several aspects of the large-scale atmospheric circulation have likely changed since the mid-20th century, but limited proxy evidence yields low confidence in how these changes compare to longer-term climate. The Hadley circulation has likely widened since at least the 1980s, and extratropical storm tracks have likely shi...

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“…Our results are consistent with those of global climate model based studies. This is consistent with the common statement that implies that ALB is the most important biogeophysical driver of LULCC effects and this statement holds only for global climate aspects and not for local effects (Gulev et al, 2021).…”

Fluctuating Atlantic inflows modulate Arctic atlantification

“…Satellite ice thickness estimates are for the Arctic south of 88°N. Thickness estimates from more localized airborne/ground electromagnetic surveys near the North Pole (diamonds) and from Operation IceBridge (circles) are shown within the context of the larger scale changes in the submarine and satellite records ( 52 ). EM, electromagnetic.…”

Water regime and fertilizer‐phosphorus source effects on greenhouse gas emissions from rice

“…Different irrigation regimes in rice production systems can have a significant impact on greenhouse gas (GHG) emissions. Rice cultivation alone contributes between 6% and 11% of the total global methane (CH 4 ) emissions to the atmosphere (Gulev et al, 2021). Nitrogenous fertilizer applications and cropping practices are responsible for nearly 75% of nitrous oxide (N 2 O) emissions in the United States (USEPA, 2023).…”