The State of the Climate 2021 - Highlighted Article

From: The Global Warming Policy Foundation

By: Ole Humlum

Date: April 2022

The State of the Climate 2021

General overview 2021

This report has its main focus on observations and not on the output of numerical models, with the exception of Figure 39 (see p. 38). References and data sources are listed at the end of the report.

Air temperatures

Air temperatures measured near the planet’s surface (surface air temperatures) are at the centre of many climate discussions, but the significance of any short-term warming or cooling should not be overstated. Whenever the Earth experiences warm El Niño or cold La Niña episodes, major heat exchanges take place between the Pacific Ocean and the atmosphere above, eventually showing up as a signal in the global air temperature. However, such heat exchanges may chiefly reflect redistribution of energy between ocean and atmosphere, and not a change in the heat content of the atmosphere–ocean system. Evaluating the dynamics of ocean temperatures is therefore just as important as evaluating changes in surface air temperatures.

Considering surface air temperature records since the 19th century, 2021 was a warm year, but cooler than most years since 2016. A moderate La Niña episode played out during 2021, underlining the importance of ocean–atmosphere exchanges.

Many Arctic regions experienced record high air temperatures in 2016, but since then, including in 2021, conditions have generally moved toward somewhat cooler conditions. The temperature peak in high northern latitudes in 2016 may have been affected by ocean heat released from the Pacific Ocean during the strong 2015–16 El Niño and subsequently transported towards the Arctic region. This underscores how air temperatures may be affected, not only by variations in local conditions, but also by variations playing out in geographically remote regions.

Many figures in this report focus on the period since 1979 – the satellite era – when access to a wide range of observations with nearly global coverage, including temperature, became commonplace. These data provide a detailed view into temperature changes over time at different altitudes in the atmosphere. Among other phenomena, these observations reveal that a Stratospheric temperature plateau has prevailed since 1995.

Since 1979, lower Troposphere temperatures have increased over both land and oceans, but most clearly over the land. The most straightforward explanation for this is that much of the warming is caused by solar insolation, but there may be several secondary reasons, such as changes in cloud cover and land use.

Oceans ... (continue reading)

The State of the Climate 2021