The climate is not warming but sea level is rising: a paradox?

The balance of evidence suggests that the climate is not warming appreciably, contrary to expectations. A U.S. National Research Council report ["Reconciling Observations of Global Temperature Change." National Academy Press. Washington, DC., Jan. 2000] has highlighted but not explained the disparity between different data sets: While a variety of surface thermometers report a substantial warming trend, microwave sensing units (MSU) on weather satellites, and also radiosondes carried in weather balloons, show little if any warming of the atmosphere in the last twenty years. As is well understood, however, climate models predict the exact opposite, namely a stronger warming trend for the atmosphere than for the surface.

After further investigating this puzzling discrepancy involving different observing methods as well as theoretical models, we hypothesize that the recent surface warming trend may not be credible. We note that while there is general agreement that the global climate warmed before 1940, and then cooled slightly until about 1975, the well-controlled surface temperature data for the United States and for Europe do not show any appreciable post-1940 warming, after correction for local urban warming ("heat islands"). This lack of warming throws further doubt on the reported global surface trend reported by teh UN-IPCC (Intergovernmental Panel on Climate Change).

Further, proxy temperature data from tree rings, ice cores, etc. show no post-1940 warming trends either; many even show a cooling trend after 1940. The observations of Arctic sea-ice shrinking, deep-ocean warming, and glacier-length changes can be readily explained as a delayed consequence of pre-1940 climate warming; they are all in good accord with the hypothesis that the Earth's climate has not warmed appreciably in the past 60 years.

In particular, we can show that the rise in sea level during the 20th century, about 18 cm (7 inches), is simply part of the ongoing trend that has raised the level by 120 meters (400 feet) since the peak of the last ice age some 18,000 years ago. Unless a new ice age intervenes, we expect this same trend to continue for the next 5000 years or so as a result of the slow melting of Antarctic ice sheets, irrespective of any human activities.