North American Climate Extremes Monitoring

Introduction

Extreme weather and climate events—such as drought, heavy rain, and heat waves—are a natural part of the Earth's climate system. Nonetheless, extreme weather and climate events can have significant impacts on our lives and on the environment. In a non-changing climate, society and the environment are more likely to be resilient to weather and climate extremes as they acclimate to the historical range of extremes. However, as the climate changes these extremes may occur outside the historical range, resulting in societal and environmental vulnerabilities.

Certain weather and climate extremes are expected to become more frequent during the 21st century. According to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (IPCC, 2007), "confidence has increased that some weather events and extremes will become more frequent, more widespread or more intense during the 21st century". Thus monitoring and analyzing climate extremes is an important component of assessing the climate system and has received a great deal of attention, especially because the impacts of climate-related changes can vary among regions.

Changes in extremes across North America have already been observed in recent decades. According to the U.S. Climate Change Science Program (CCSP, 2008), "most of North America has been experiencing more unusually hot days and nights, fewer unusually cold days and nights and fewer frost days. Heavy downpours have become more frequent and intense. Droughts are becoming more severe in some regions". The North American Climate Extremes Monitoring (NACEM) product was developed to provide an accessible analysis tool that will help improve the understanding of observed changes in extreme climate conditions by providing users the ability to examine trends and occurrences of certain types of extreme or threshold events at the station-by-station level.

The NACEM currently provides data and analysis for eight indices that have been defined by the World Meteorological Organization (WMO) Commission for Climatology/CLIVAR Expert Team on Climate Change Detection Monitoring and Indices (ETCCDMI). Additional indices will be added to the NACEM at a later time. The NACEM computes each available index at the station-level and provides corresponding anomalies, data permitting, with respect to the 1961–90 long-term average. An interactive map allows users to select a month, season, or specific year (from 1955 to present) to view a snapshot of values for a specific index across North America. There is also an option to view time series graphics for a station of interest by simply selecting the station.