RECENT PAST CLIMATE CHANGE

What are climate change records?

To understand the world's climate and how it was changed, there are many measurements that scientist have to evaluate.

An obstacle in evaluating past climate change is the fact that a lot of observations are not complete. Climate observations were mainly limited to weather situations and ships, and included measurements made near the land or ocean surface. 

In recent years things have improved, ballon soundings have been widespread over the land, satellites have covered all world and there has been an increase in sub-surface monitoring.

But there are no records of measurements bafore 1600s so scientifics have to use other types of information to investigate further back. These kind of data are called indirect or proxy measurements.

They use the tree-rings to determinate the chages in temperature and precipitation. A tree grows and it adds a new ring around its waistline each year so climate conditions have influence in the tree-ring widths.

The ice-cores have accumulated from snowfall over many millennia so, ice cores can tell to scientifics about temperature, precipitation, volcanic activity and wind patterns.

Coral reefs can be used to obtain measurements about temperature and sea-level changes. Corals build their hard skeletons form calcium carbonate. The calcium carbonate contains isotopes of oxygen that can be used to determine the temperature of the water in wich the coras grews.

Finally, scientist can use the polen grains to identify the type of plant from which they came and identify at what time the sediment, where the pollen laid, was deposited.

Sources:  http://www.ncdc.noaa.gov/news/what-are-proxy-data

How volcanos have influence in climate change?

During this week we have seen that the gases and dust particles thrown into the atmosphere during volcanic eruptions have influences on climate.

Volcanic ash or dust released into the atmosphere during an eruption shade sunlight and cause temporary cooling. Larger particles let sunlight in but do not let heat radiation from the Earth’s surface out, and the result is a warmer Earth. Small ash particles form a dark cloud in the troposphere that block some of the incoming energy from the Sun and the Earth cools. Most of these particles fall out of the atmosphere within rain a few hours or days after an eruption. But the smallest particles of dust get into the stratosphere and are able to travel vast distances, often worldwide. These tiny particles are so light that they can stay in the stratosphere for months, blocking sunlight and causing cooling over large areas of the Earth.

Another component has influence in the climate change. Often, erupting volcanoes emit sulfur dioxide into the atmosphere. The sulfur dioxide moves into the stratosphere and combines with water to form sulfuric acid aerosols. The sulfuric acid makes a haze of tiny droplets in the stratosphere that reflects incoming solar radiation, causing cooling of the Earth’s surface. The aerosols can stay in the stratosphere for up to three years, moved around by winds and causing significant cooling worldwide. Eventually, the droplets grow large enough to fall to Earth.

Sources:
http://earthobservatory.nasa.gov/Features/Aerosols/

http://volcano.oregonstate.edu/how-do-volcanoes-affect-atmosphere-and-climate
http://scied.ucar.edu/shortcontent/how-volcanoes-influence-climate


How is today’s warming different from the past?

The Earth’s climate changed due to natural causes in the past. Most often, global climate has changed because of variations in sunlight, the effect of volcanic eruptions, variations in the Earth's orbit and fluctuations in the energy that the sun emits. 

These natural causes have influence today but too small compared to human activity. For example, although volcanoes continue to emit carbon dioxide, the amount of carbon dioxide is extremely small compared to human emission because the world population is a little over a trillion today which implies that carbon dioxide emissions have considerably increased.

Sources: http://earthobservatory.nasa.gov/Features/GlobalWarming/page3.php


What is the role of isotopes in determining temperatures from the past?

The carbonate is the key to know about past temperatures. Originally, carbote is dissolved in the oceans and it forms the shell of a little sea animal, the foraminifera. Studying the shell of this animal through the carbonate that forms it, scientifics can discover how temperatures have changed.

Carbonate contains oxygen, whose atoms exist in two naturally-occurring stable isotopes, ¹⁸O and ¹⁶O.The ratio of these two isotopes in the shells tells us about past temperatures.

The variability of ¹⁸O in the ocean determinates the temperature. This way, when water evaporates in warm climates, the molecules of ¹⁶O tends to evaporate first, so it has more ¹⁸O in places where lots of water evaporates and less where it rains a lot.
¹⁸O isotope is the first to back down into the oceans in form of precipitation, therefore shells have high levels of this isotope.

Changes in climate that alter the global patterns of evaporation or precipitation can therefore cause changes to the background δ¹⁸O ratio.  

Sources: http://www.giss.nasa.gov/research/briefs/schmidt_01/


How have trees been used to reconstruct different climate variables across the world?

Dendrochronology or tree-ring dating is the method of scientific dating based on the analysis of tree ring growth patterns. Tree rings vary in width denpendent on fast or slow growth patterns during warm or cold periods. the density of cells reflects on the growth patterns (low density results in thin rings, high density produces thick rings). Tree could also have diseases or additional enrichment, which result in the varying growth patterns also.

Tree-rings can provide continuous yearly paleoclimatic records for regions or periods of time with no instrumental climate data. However, different species respond to different climate parameters. Scientifics have to consider when dating trees that most trees are not old enough, so the records do not date back as far as other sources of climate data. This is when crossdating is important to identify similar growth patterns across many trees and make a longer timeline of climate data.This way, increasing the amount of trees utilised to study, the best crossdating results can be obtained.

Sources:
http://web.utk.edu/~grissino/principles.htm#1
http://www.windows2universe.org/earth/climate/CDcourses_treerings.html
https://www.ncdc.noaa.gov/news/picture-climate-how-can-we-learn-tree-rings

How can ice cores provide a record of atmospheric composition?

The most important property of ice cores is that they are a direct archive of past atmospheric gasses. Air is trapped at the base of the firn layer, and when the compacted snow turns to ice, the air is trapped in bubbles.The air bubbles are extracted by melting, crushing or grating the ice in a vacuum.This method provides detailed records of carbon dioxide, methane and nitrous oxide going back over 650,000 years

Also, it is possible to discern past air temperatures from ice cores. This can be related directly to concentrations of carbon dioxide, methane and other greenhouse gasses preserved in the ice. The ratio of oxygen isotopes in the snow reveals temperature, though in this case, the ratio tells how cold the air was at the time the snow fell. In snow, colder temperatures result in higher concentrations of light oxygen.

Sources:
http://www.antarcticglaciers.org/glaciers-and-climate/ice-cores/ice-core-basics/
http://www.earthobservatory.nasa.gov/Features/Paleoclimatology_IceCores/