The IPCC predictions from 1990 went for a probable rise of the global mean temperature of 0.3 °C per decade and at least 0.2 °C per decade. See the IPPC assessment overview document, Section 1.0.3. (It is available online here.) We have had two decades. Fact: they predicted more warming than what actually materialized. Quite a bit more. See:
• Instrumental temperature record, Wikipedia.
What’s the full story here? Here are some basic facts. The policymaker summary of the 1990 report estimates:
under the IPCC Business-as-Usual (Scenario A) emissions of greenhouse gases, a rate of increase of global-mean temperature during the next century of about 0.3 °C per decade (with an uncertainty range of 0.2 °C to 0.5 °C per decade); this is greater than that seen over the past 10,000 years. This will result in a likely increase in global-mean temperature of about 1°C above the present value by 2025 and 3°C before the end of the next century. The rise will not be steady because of the influence of other factors…
I believe we are going along with the ‘business-as-usual’ emissions of greenhouse gases. On the other hand, Wikipedia shows a figure from Global Warming Art:
based on NASA GISS data here. In 1990, the 5-year mean Global Land-Ocean Temperature Index was .27, meaning .27 °C above the mean temperature from 1961 to 1990. By 2006, the 5-year mean was .54.
So, that’s a .27 °C increase in 16 years, or about .17 °C per decade. This is slightly less than the bottom-end estimate of 0.2 °C per decade, and about half the expected rise of 0.3 °C per decade.
Is there any official story on why the 1990 IPCC report overestimated the temperature rise during this time? In 2007 the IPCC estimated a temperature rise of about 0.2 °C per decade for the next two decades for all the scenarios they considered. So, it seems somehow 0.3 °C went down to 0.2 °C. What was wrong with the original estimate?