2-9: Trends in Climate Variables, Global Warming Update

© Eugene S. Takle
2000, 2002, 2005, 2006

Introduction

A review of the US climate patterns for 2006 is given by the National Climatic Data Center (NCDC), and the review of global patterns of change for 2005 are put into perspective of the entire instrumental record. You should read through this summary to get an overall record of the global mean temperature patterns for the last 127 years.

Global Temperatures

Trends in global mean surface temperatures are best revealed by plotting temperature "anomalies," which are changes from the long-term (120 year) average over the period for which we have instrument records.

Global land, ocean, and land-ocean combined surface data (Figure 1) show that the last 4-5 years have been near the record high year of 1998 (an El Niño year). The high temperatures in recent years are observed both over oceans and over land.

Global mean surface temperatures have increased over the past 120 years at a reate near 0.06 C/decade (0.11 F/decade) but with periods of larger and smaller trend. During the past 25 to 3- years this trend has approximately 0.18 C/decade (0.32 F/decade). The most recent period of increasing surface temperatures has a warmning rate comparable to the rates of warming projected by the global climate models using observed changed in greenhouse gases, statospheric ozone concentration, volcanoes, and fluctuations of the output of the sun. This recent trend is expected to continue throughout the next century with continued increases of anthropogenic greenhouse gases.

Temperature measurements above the Eath's surface have been made over the past 50 to 60 years using balloon-borne instruments (radiosondes) and for the past 28 years using satellites. These measurements show that the middle tropospheric temperatures (14 to 22 km above the surface) have been below average since the dissipation of the warming effects from the 1991 Mt. Pinatubo eruption. Depletion of the ozone in the lower statosphere, combine with the effects of rising greenhouse gas concentrations, would lead to lower temperatures int eh stratosphere of magnitude consistent with these observations.

Global Precipitation

Global mean precipitation over the past 100 years shows a weak resemblance to global temperature history (low at the beginning of the record, increasing beginning in the 1940s, variable to 1980, and increasing since then. A global distribution of change from 1900-1994 generally shows increases at high latitudes and decreases in subtropical areas.

Identifying Climate Change

Over the US, the best record we have for tracking climate change is the United States Historical Climatology Network comprised of 1, 221 high-quality stations from the U.S. Cooperative Observing Network within the 48 contiguous United States. This USHCN web site also gives information on quality control and adjustment procedures for reducing biases in the datasets. A wealth of additional climate data can be found online at the NCDC . NCDC has prepared answers to a number of very timely questions:

• Is the climate warming?
• Are El Ninos related to Global Warming?
• Is the hydrological cycle (evaporation and precipitation) changing?
• Is the atmospheric oceanic circulation changing?
• Is the climate becoming more variable or extreme?
• How important are these changes in a longer-term context?
• Is sea level rising?
• Can the observed changes be explained by natural variability?

The global equivalent of the USHCN is the Global Historical Climate Network. To get information from this source you must agree to a data-use policy of NOAA and the World Meteorological Organization. This is an example of the current political debate of fair use of global environmental data. After agreeing to the fair-use policy you will gain access to the Global Historical Climate Network. The precipitation network shows dense coverage over most developed countries. Regions of sparse measurements include northern Canada, Siberia, central Australia, Sahara Desert, Greenland and Antarctica. The network of daily mean temperatures is quite similar to the precipitation network, but the distribution of stations measuring both daily maximum and daily minimum temperatures is considerably more sparse. Note particularly the lack of maximum and minimum temperatures over South America.

The Debate Over Evidence

The debate over whether or not the atmosphere is warming has been quite intense since the late 1990s. Satellite records, with a more limited period than surface temperatures, suggested that the rapid warming in since 1970 might be artificial, but a subsequent re-calibration of the temperature data eliminated the differences in the two records. The "Summary for Policy Makers" of the Intergovernmental Panel on Climate Change Fourth Assessment Report issued in February 2007 produced a strongly worded statement about the role of humans in climate change:
"Changes in climate are now affecting physical and biological sysems on every continent. Effects on human systems, although more difficult to discern due to adaptation and non-climatic drivers, are emerging. Over 99% of obeserved changes in systems and sectors are consisten with regional temperature trends. Many of the changes are now attributed to temperature increase caused by anthropogenic greenhouse gas emissions."