Climatechange1

Uncertainty in the projected changes

There is uncertainty in climate change modelling.  Uncertainty refers to a state of having limited knowledge. Uncertainty can result from lack of information or from disagreement over what is known or even knowable. Uncertainty may arise from many sources, such as quantifiable errors in data, or uncertain projections of human behaviour. Uncertainty can be represented by quantitative measures or by qualitative statements.

Uncertainty in climate change projections is a major problem for those planning to adapt to a changing climate. Uncertainty in projections of future climate change arises from three principal causes:

  • natural climate variability;
  • modelling uncertainty, referring to an incomplete understanding of Earth system processes and their imperfect representation in climate models; and
  • uncertainty in future emissions

More information is available from the UK Climate Impacts Programme website: http://ukclimateprojections.defra.gov.uk/23191

 

Unpredictability–What is the difference between weather and climate?

Weather is the day-to-day state of the atmosphere, and its short-term variation in minutes to weeks. People generally think of weather as the combination of temperature, humidity, precipitation, cloudiness, visibility, and wind. We talk about changes in weather in terms of the near future: “How hot is it right now?”, “What will it be like today?” and “Will we get a snowstorm this week?”

Climate is the weather of a place averaged over a period of time, often 30 years. Climate information includes the statistical weather information that tells us about the normal weather, as well as the range of weather extremes for a location.

We talk about climate change in terms of years, decades, and centuries. Scientists study climate to look for trends or cycles of variability, such as the changes in wind patterns, ocean surface temperatures and precipitation over the equatorial Pacific that result in El Niño and La Niña.  They also research how cycles like El Niño, La Niña and other phenomena fit into the bigger picture of possible longer term or more permanent climate changes.

 

Forecasting weather and predicting climate

Weather forecasters try to answer questions like: “What will the temperature be tomorrow?” “Will it rain?” “How much rain will we have?” and “Will there be thunderstorms?”  Today, most weather forecasts are based on models, which incorporate observations of air pressure, temperature, humidity and winds to produce the best estimate of current and future conditions in the atmosphere. A weather forecaster then looks at the model output to figure out the most likely scenario.  The accuracy of weather forecasts depend on both the model and on the forecaster’s skill. Short-term weather forecasts are accurate for up to a week. Long-term forecasts, for example seasonal forecasts, tend to use statistical relationships between large-scale climate signals such as El Niño and La Niña and precipitation and temperature to predict what the weather will be like in one to six months time.

Climate predictions take a much longer-term view.  These predictions try to answer questions like: “How much warmer will the Earth be 50 to 100 years from now?” “How much more precipitation will there be?” and “How much will sea level rise?” Climate predictions are made using global climate models. Unlike weather forecast models, climate models cannot use observations because there are no observations in the future.

Source: Text from the National Snow and Ice Data Centre