RealClimate logo

Note 3/23/2021: we had a few hiccups with comments after moving the site to https/SSL. Hopefully they're fixed now. Please let us know if there are remaining issues.

A potential rule of thumb for hourly rainfall?

Future global warming will be accompanied by more intense rainfall and flash floods due to increased evaporation, as a consequence of higher surface temperatures which also lead to a higher turn-around rate for the global hydrological cycle. In other words, we will see changing rainfall patterns. And if the global area of rainfall also shrinks, then a higher regional concentration of the rainfall is bound to lead to more intense downpours (the global rainfall indicator is discussed here). 

More »

IPCC Special Report on Land

Thread for discussions of the new special report. [Boosting a comment from alan2102].

Climate Change and Land
An IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems

Land degradation accelerates global climate change. Al Jazeera English
Published on Aug 8, 2019

New UN report highlights vicious cycle of climate change, land degradation. CNA
Published on Aug 8, 2019

New IPCC Report Warns of Vicious Cycle Between Soil Degradation and Climate Change. The Real News Network
Published on Aug 8, 2019

Alpine glaciers: Another decade of loss

Filed under: — group @ 25 March 2019

Guest Commentary by Mauri Pelto (Nichols College)

Preliminary data reported from the reference glaciers of the World Glacier Monitoring Service (WGMS) in 2018 from Argentina, Austria, China, France, Italy, Kazakhstan, Kyrgyzstan, Nepal, Norway, Russia, Sweden, Switzerland and United States indicate that 2018 will be the 30th consecutive year of significant negative annual balance (> -200mm); with a mean balance of -1247 mm for the 25 reporting reference glaciers, with only one glacier reporting a positive mass balance (WGMS, 2018).

A view of how alpine glaciers in the Pacific Northwest fit into the broader ecosystem (Megan Pelto, Jill Pelto).
More »


Climate indicators

The climate system is complex, and a complete description of its state would require huge amounts of data. However, it is possible to keep track of its conditions through summary statistics.

There are some nice resources which give an overview of a number for climate indicators. Some examples include NASA and The Climate Reality Project.

The most common indicator is the atmospheric background CO2 concentration, the global mean temperature, the global mean sea level, and the area with snow or Arctic sea ice. Other indicators include rainfall statistics, drought indices, or other hydrological aspects. The EPA provides some examples.   

One challenge has been that the state of the hydrological cycle is not as easily summarised by one single index in the same way as the global mean temperature or the global mean sea level height. However, Giorgi et al. (2011) suggested a measure of hydro-climatic intensity (HY-INT) which is an integrated metric that captures the precipitation intensity as well as dry spell length.  

There are also global datasets of indices representing the more extreme aspects of climate called CLIMDEX, providing a list of 27 core climate extremes indices (so-called the ‘ETCCDI’ indices, referring to the ‘CCl/CLIVAR/JCOMM Expert Team on Climate Change Detection and Indices’).

In addition, there is a website hosted by the NOAA that presents various U.S. Climate Extremes Index (CEI) in an interactive way.

So there are quite a few indicators for various aspects of the climate. One question we should ask, however, is whether they capture all the important and relevant aspects of the climate. I think that they don’t, and that there are still some gaps.

More »


  1. F. Giorgi, E. Im, E. Coppola, N.S. Diffenbaugh, X.J. Gao, L. Mariotti, and Y. Shi, "Higher Hydroclimatic Intensity with Global Warming", Journal of Climate, vol. 24, pp. 5309-5324, 2011.

Why extremes are expected to change with a global warming

Filed under: — rasmus @ 5 September 2017

Joanna Walters links extreme weather events with climate change in a recent article in the Guardian, however, some  reservations have been expressed about such links in past discussions.

For example, we discussed the connection between single storms and global warming in the post Hurricanes and Global Warming – Is there a connection?, the World Meteorological Organization (WMO) has issued a statement, and Mike has recently explained the connection in the Guardian.

More »

New report: Climate change, impacts and vulnerability in Europe 2016

Filed under: — rasmus @ 6 February 2017

Another climate report is out – what’s new? Many of the previous reports have presented updated status on the climate and familiar topics such as temperature, precipitation, ice, snow, wind, and storm activities.

The latest report Climate change, impacts and vulnerability in Europe 2016 from the European Environment Agency (EEA) also includes an assessment of hail, a weather phenomenon that is often associated with lightening (a previous report from EASAC from 2013 also covers hail).

Usually, there has not been a lot of information about hail, but that is improving. Still, the jury is still out when it comes to hail and climate change:

Despite improvements in data availability, trends and projections of hail events are still uncertain.

More »

Another fingerprint

Filed under: — rasmus @ 20 May 2012

When my kids were younger, they asked me why the ocean was blue. I would answer that the ocean mirrors the blue sky. However, I would not think much more about it, even though it is well-known that the oceans represent the most important source for atmospheric moisture. They also play an important role for many types of internal variations, such as the El Nino Southern Oscillation. Now a new study by Durack et al. (2012) has been published in Science that presents the relationship between the oceans and the atmosphere.

More »


  1. P.J. Durack, S.E. Wijffels, and R.J. Matear, "Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000", Science, vol. 336, pp. 455-458, 2012.