File Name: long and short time scale changes to the earth .zip
Weather is the state of the atmosphere—its temperature, humidity, wind, rainfall and so on—over hours to weeks.
Milankovitch cycles describe the collective effects of changes in the Earth 's movements on its climate over thousands of years. In the s, he hypothesized that variations in eccentricity , axial tilt , and precession resulted in cyclical variation in the solar radiation reaching the Earth, and that this orbital forcing strongly influenced the Earth's climatic patterns. Similar astronomical hypotheses had been advanced in the 19th century by Joseph Adhemar , James Croll and others, but verification was difficult because there was no reliably dated evidence, and because it was unclear which periods were important. Now, materials on Earth that have been unchanged for millennia obtained via ice , rock , and deep ocean cores are being studied to indicate the history of Earth's climate. Though they are consistent with the Milankovitch hypothesis, there are still several observations that the hypothesis does not explain.
In order to understand climate change, we must understand climate variability. This module will outline some key concepts such as weather, climate variability and of course, climate change. Weather describes current atmospheric conditions, such as rainfall, temperature, and wind speed, at a particular place and time. It changes from day to day. Changes in climate are hard to detect without very long-term records. One way to understand the difference between weather, climate variability and climate change is to think about how they operate on different time scales.
We can see here that weather refers to hours, days and maybe months; climate refers to months, years and decades, and climate change refers to decades and centuries. Examples of weather are rain storms that might last one or two hours and tropical cyclones that may last days. Figure 1: A guide to the timescales applicable to weather, climate variability and climate change.
We are now going to take a closer look at the each of these timescales. The graph in Figure 2 shows an example of the changes in air temperature over five days. Some days are warmer than others and there is variability from hour to hour. The graph in Figure 3, the time scale has been expanded to show temperature changes over five years. The temperature is shown in degrees Celsius on the y-axis and the years are shown on the x-axis. The black rectangle shows a five-day period similar to that shown in Figure 2.
The blue line shows the daily temperature variation and the red line shows the average daily temperature over the five years. Daily temperatures vary greatly but the daily averages clearly show that some parts of the year are regularly warmer than others. These seasonal cycles are an example of a temperate climate with four distinct seasons: summer, autumn, winter and spring. Figure 3: Example air temperature over five years the black rectangle shows a five-day period like that shown in Figure 2.
You can see how summer temperatures are higher and winter temperatures are lower in some years than others due to natural variation. However, if we want to understand the general climate of this area, we need to consider a longer time period such is shown in Figure 4.
Over a longer period, such as 50 years see Figure 4 , we can see the year to year variability more clearly. We can calculate the long term mean, or average climate and we can see whether there is a trend in the mean climate. In this example there is a warming trend identified by the black line going up.
This shows an increase of more than one degree Celsius over fifty five years. This is not what would be expected under normal conditions and is very likely an indication that the climate is changing. It should be noted however, that even though there is a gradual overall warming trend over the fifty years, the situation can appear quite different if we look at shorter periods.
The short blue lines show that some 10 year periods show a decrease a while others show a more dramatic increase b in temperature. Figure 4: Example air temperature over 50 years the black rectangle shows a five-year period like that shown in Figure 3. It is strongest in the Southern Hemisphere wet season. The Intertropical Convergence Zone stretches across the Pacific just north of the equator and is strongest in the Northern Hemisphere wet season.
The West Pacific Monsoon is driven by large differences in temperature between the land and the ocean. It moves north to mainland Asia during the Northern Hemisphere summer and south to Australia in the Southern Hemisphere summer.
The seasonal arrival of the Monsoon usually brings a switch from very dry to very wet conditions. Figure 5: The main influences on the climate of the Pacific Region, shown here in their long-term average November to April positions.
ENSO affects the strength and position of the main climate features, leading to variability in rainfall, temperature, winds, cyclone activity, ocean currents and sea level. During the Southern Hemisphere wet season, the heaviest rainfall occurs in the monsoon region and in the South Pacific Convergence Zone.
The map in Figure 6 shows the long term mean climate of the Southern Hemisphere wet season rainfall and surface winds. The wind is shown by the arrows. Figure 6: Long term mean rainfall and wind in the Southern Hemisphere wet season over the Pacific.
Also, high rainfall can be seen over the western Pacific because of the West Pacific Monsoon. Winds converge to form the South Pacific Convergence Zone. In contrast, the climate of the Southern Hemisphere dry season Figure 7 has the heaviest rainfall in the monsoon region and the Inter-Tropical Convergence Zone. Figure 7: Long term mean rainfall and wind in the Southern Hemisphere dry season over the Pacific.
As we have seen, climate variability describes short-term changes in climate that take place over months, seasons and years. This variability is the result of natural, large-scale features of the climate that we looked at earlier.
The different phases of ENSO can cause droughts and floods. The trade winds white arrows blow to the west and cause a build up of warm surface water orange-red areas and higher sea level in the West Pacific. The warm water heats the air above it, making the moist air rise and forming clouds this is called convection.
This warmer air then moves east to where the air is cooler, the cooler air sinks towards the surface and moves west, creating a convective circulation.
These include:. The greenhouse effect is a natural process that makes our planet liveable. The greenhouse gases in the atmosphere can be compared to the walls of a greenhouse, keeping the heat in. These greenhouse gases include: water vapour, carbon dioxide CO 2 , methane, nitrous oxide and some industrial gases such as chlorofluorocarbons CFCs. Water vapour and carbon dioxide are the most important greenhouse gases.
The amount of warming depends on various feedback mechanisms. As can be seen in Figure 11, current atmospheric concentrations of carbon dioxide in red far exceed pre-industrial values pre values. This has been determined in part by analysing the air trapped in ice cores spanning the past , years.
The inset picture shows air bubbles trapped in an ice core taken from Antarctica - this air has been tested for levels of C0 2.
The graph shows carbon dioxide levels are now rising at a very fast rate. During the s, the amount of carbon dioxide in the air rose by less than 1 part per million per year. From —, the growth rate increased to more than 2. Carbon dioxide concentrations are now greater than at any time during the past , years. The rate of increase is accelerating.
At the same time as carbon dioxide is increasing in the atmosphere, the earth is warming. The climate system is currently warmer than at any time during the past years, and perhaps the warmest it has been for a million years. This is consistent with the increases in carbon dioxide emissions.
Inset: ice-core sample showing trapped air bubbles. Increased concentrations of greenhouse gases in the atmosphere due to human activities are most likely the underlying cause of warming in the 20 th century. As we put greenhouse gases into the atmosphere, this creates warming, and a lot of this heat goes into the ocean. The chart in Figure 13 shows that most of the extra heat from global warming is being absorbed by the oceans and only very small amounts are absorbed by land masses and the atmosphere.
This results in changes to the ocean which we will look at in the next section. Figure Heat content of the ocean, land and atmosphere from to the early s. Note that almost all of the added heat has gone into the ocean. As water warms it expands. Added to this, glaciers and ice sheets melt as the atmospheric temperature increases.
These two factors, expanding warmer water and ice melt, result in sea level rise. Observations of sea level rise from tide gauges over the 20 th century show a global average sea level rise of 1.
The graph in Figure 14 shows global average sea level since The solid blue line is based on tide gauge data and the red line is sea level measured by satellites. Since the rate of rise measured by satellite altimeters has been about 3.
Sea level rise is a challenge for low lying areas. Figure Global average sea level since derived from tide gauge data blue line and satellite data red line. The ocean absorbs about one quarter of the annual emission of CO 2 resulting from human activities. This is good in that it slows the rate of atmospheric warming but the consequence is ocean acidification. When the CO 2 is taken up by the ocean, it combines with the seawater to produce carbonic acid, a weak acid Figure The ocean is alkaline but the addition of carbonic acid reduces the alkalinity.
As a result, many key species in tropical ecosystems, including reef building corals, show a reduced capacity to grow calcium carbonate skeletons and shells. Ocean acidification could have serious consequences for these reef ecosystems which are already stressed by global warming and other pressures like fishing. This will in turn impact industries such as coastal fisheries and others that depend on marine resources. Figure Carbon dioxide is absorbed by the oceans leading to a change in the water chemistry.
Source: Hoegh-Guldberg et al. The climate has changed across the Pacific region and while there is considerable variation from country to country, there are some general similarities across the region. Temperature has warmed at all locations in the Pacific, with Pacific island annual temperature trends ranging between 0. Rainfall across the region has increased and decreased in response to natural climate variability but over the last 50 years, rainfall totals have increased to the north-east of the South Pacific Convergence Zone and declined to the south.
There have been significant changes to the ocean too with acidification increasing across the region, Sea level has risen, however there are differences across the region. This module has outlined some of the key aspects of both climate variability and climate change. Climate is the long term average of weather, and climate variability acts on different timescales. ENSO is the most important driver of year to year variability in the region.
The geologic time scale GTS is a system of chronological dating that classifies geological strata stratigraphy in time. It is used by geologists , paleontologists , and other Earth scientists to describe the timing and relationships of events in geologic history. The time scale was developed through the study of physical rock layers and relationships as well as the times when different organisms appeared, evolved and became extinct through the study of fossilized remains and imprints. The table of geologic time spans, presented here, agrees with the nomenclature , dates and standard color codes set forth by the International Commission on Stratigraphy ICS. The primary and largest catalogued divisions of time are periods called eons. The first eon was the Hadean , starting with the formation of the Earth and lasting over million years until the Archean , which is when the Earth had cooled enough for continents and the earliest known life to emerge.
In order to understand climate change, we must understand climate variability. This module will outline some key concepts such as weather, climate variability and of course, climate change. Weather describes current atmospheric conditions, such as rainfall, temperature, and wind speed, at a particular place and time. It changes from day to day. Changes in climate are hard to detect without very long-term records.
Models that account only for the effects of natural processes are not able to explain the warming observed over the past century. Models that also account for the greenhouse gases emitted by humans are able to explain this warming. Click the image to view a larger version. When incoming energy from the sun is absorbed by the Earth system, Earth warms.
The atmosphere is a dynamic fluid that is continually in motion. Both its physical properties and its rate and direction of motion are influenced by a variety of factors, including solar radiation , the geographic position of continents , ocean currents , the location and orientation of mountain ranges, atmospheric chemistry , and vegetation growing on the land surface. All these factors change through time. Some factors, such as the distribution of heat within the oceans , atmospheric chemistry, and surface vegetation, change at very short timescales. Others, such as the position of continents and the location and height of mountain ranges, change over very long timescales.
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. Such variability influences society through a multitude of impacts while operating over a continuum of time scales, from seasonal through centennial and longer. Variability in climate the time-averaged weather manifests itself in a variety of forms, such as trends, cycles, and complex regional interactions.
Fracking is a controversial form of drilling that uses high-pressure liquid to create cracks in underground shale to extract natural gas and petroleum. Carbon emissions from fossils fuels like these have been linked to global warming and climate change. Climate is sometimes mistaken for weather. But climate is different from weather because it is measured over a long period of time, whereas weather can change from day to day, or from year to year. The climate of an area includes seasonal temperature and rainfall averages, and wind patterns. Different places have different climates.
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It extends the time scale of climate changes over the entire history of Earth to the term „climatic change‟ to encompass all forms of climatic variability on The Earth‟s atmospheric circulation is the large-scale movement of.Bruce L. 11.06.2021 at 09:11
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