Fluctuations in some climate parameters

There is argument as to the extent to which there has been an increase over the past few decades in the frequency of the extremes of climatic parameters, such as temperature, storminess, precipitation, etc, an obvious point being that Global Warming might be responsible. Here we report results on those parameters of which we have had experience during the last few years: Global surface temperature, Cloud Cover and the MODIS Liquid Cloud Fraction. In no case we have found indications that fluctuations of these parameters have increased with time.

💡 Research Summary

The paper “Fluctuations in some climate parameters” investigates whether the variability of key climate variables—global surface temperature, low‑level cloud cover (LCC), and MODIS‑derived liquid cloud fraction (LCF)—has increased over recent decades, a question often linked to anthropogenic global warming. The authors define a “fluctuation” as the deviation of an observed value from a low‑order polynomial (3‑ or 6‑degree) fit to its temporal series, and they quantify this deviation using the root‑mean‑square (RMS) metric.

Data sources are: (1) the GISS‑NASA surface temperature record (1880–2010), (2) the International Satellite Cloud Climatology Project (ISCCP) LCC data (available from 1983), and (3) MODIS LCF data (early 2000s onward). The globe is divided into latitude bands (typically 20° intervals) to examine spatial patterns, and the RMS values are compared with the fraction of land versus ocean in each band.

Key findings:

1. Temperature fluctuations – RMS temperature varies with latitude in a manner that mirrors the land‑to‑ocean ratio: regions with more land exhibit larger RMS values, reflecting the lower thermal inertia of land. An exception occurs above 64° N, where RMS is high despite low land fraction, likely due to regional phenomena such as the 1940s temperature peak and polar ice dynamics. When the global temperature series is split into successive 20‑year windows, the RMS shows little systematic change; if anything, it modestly declines after the 1930s. This suggests that, despite a clear rise in mean temperature (≈0.6 °C per decade since the early 1980s), the amplitude of year‑to‑year temperature deviations has not expanded.

2. Low‑level cloud cover (LCC) fluctuations – The RMS of LCC, expressed as a percentage change per year (b LCC − time), is essentially zero across all latitude bands. The authors find no statistically significant trend in cloud‑cover variability over the entire satellite record (≈20 years).

3. Liquid cloud fraction (LCF) fluctuations – Similar to LCC, the RMS of LCF shows slopes that are either indistinguishable from zero or slightly negative, indicating no increase in variability. However, the mean LCF itself declines at a rate of –0.173 % · y⁻¹, comparable to the –0.054 % · y⁻¹ decline in total cloud cover (high + mid + low). The annual peak‑to‑peak variation is about 7 % for LCF and 2.3 % for total cloud cover, confirming that the magnitude of seasonal cycles remains stable.

The authors interpret these results as evidence that, while anthropogenic greenhouse gases have raised the global mean temperature, they have not amplified the short‑term variability (i.e., the frequency of extreme temperature or cloud events) over the periods examined. The observed reduction in temperature RMS around the 1930s predates the widely cited onset of strong anthropogenic forcing (≈1950) and may reflect either an early stabilization effect or simply larger measurement uncertainties in earlier data.

Limitations acknowledged include the relatively short satellite records for cloud variables, potential confounding influences from major volcanic eruptions (e.g., Pinatubo), and sparse early temperature observations in high‑latitude regions. The authors suggest that extending analyses further back in time (e.g., using proxy reconstructions) and employing higher‑resolution regional datasets would be valuable for confirming the robustness of their conclusions.

In summary, the study concludes that (a) temperature RMS correlates with land fraction and shows a modest decline after the 1930s, (b) cloud‑cover variability has remained essentially constant over the past two decades, and (c) there is no discernible increase in the variability of the examined climate parameters since the advent of significant anthropogenic greenhouse‑gas emissions. This challenges the notion that global warming necessarily leads to more frequent extreme fluctuations, at least for the variables and time scales considered.