Biology IB HL - 4.4 Climate Change Part 3

The oceans are a major carbon sink and absorb roughly a third of all human produced (anthropomorphic) CO2 emissions

CO2 solubility is temperature dependent (more soluble when cooler), so less CO2 will be absorbed as temperatures rise

When oceans absorb atmospheric CO2, some of it will remain dissolved in a gaseous state but most will be chemically modified:

Carbon dioxide will combine with water to form carbonic acid, which dissociates into hydrogen ions and hydrogen carbonate

H+ ions will lower the ocean pH (acidification) and will also combine with free carbonate ions to form more hydrogen carbonate

With less free carbonate ions in the water, marine organisms are less able to produce calcium carbonate (via calcification)

Calcium carbonate is used to form the hard exoskeleton of coral and is also present in the shells of certain molluscs

Hence increasing concentrations of dissolved carbon dioxide threatens the viability of coral reefs and certain molluscs

Rising levels of atmospheric carbon dioxide are causing a decrease in the pH of ocean water (ocean acidification)

Since the start of the industrial revolution ocean pH has dropped from ~8.2 to ~8.1 (roughly a 30% increase in acidity)

It is predicted that if current conditions continue, oceanic pH could fall to roughly 7.8 by the turn of the century (2100)

The decrease in ocean pH is predicted to threaten the survival of marine organisms that require calcium carbonate

An increase in the concentration of H+ ions means there are less free carbonate ions available for calcification

Shells and coral exoskeletons are also likely to begin to dissolve when ocean conditions are more acidic

Experiments have shown that increasing water acidity correlates with the significant thinning of shells over several weeks

Corals, sea urchins and shelled molluscs do not exist in regions with high levels of dissolved CO2 (e.g. near hydrothermal vents)

The disappearance of coral reefs could result in a loss of shoreline protection and habitat, altering coastal ecosystems

The loss in revenue from tourism and food industries is predicted to cost economies upwards of $1 trillion by 2100

Increasing the dissolved CO2 levels in oceans would cause invasive species of algae to flourish (more photosynthesis)

Many claims have been made regarding the impact of human activities on climate change – not all are supported by evidence

Many arguments are not backed by reliable scientific data or are made by entities with vested interests (e.g. oil companies)

Climate has changed in the past and current trends merely reflect the Earth’s natural climatic cycle

Data collected from the Vostok ice core shows several changes in climate over the last 400,000 years (Figure 1)

At several points in history, global average temperatures have been warmer than those currently observed

Climate has changed in the past and current trends merely reflect the Earth’s natural climatic cycle

Climate changes do occur naturally, but usually not as abruptly as what is seen currently

When global warming occurred abruptly in the past, it was always highly destructive to life (e.g. Permian mass extinction)

Atmospheric CO2 levels positively correlate to average global temperatures and are currently at the highest levels ever recorded

Temperatures on Earth are influenced by the amount of solar radiation from the sun (more radiation = warmer temperatures)

Warmer temperatures may be caused by an increase in solar irradiance by the sun (as determined by the number of sunspots)

Climate change is being caused by solar activity and the effect of greenhouse gas emissions is negligible

Over the last 35 years the sun has shown a slight cooling trend, however average global temperatures have increased (Figure 2)

There is no evidence to support a correlation between solar irradiance and current global temperature trends

Certain changes in climate conditions cannot be linked to greenhouse gas emissions

Global sea levels began to increase before greenhouse gas emissions significantly increased following the industrial revolution

Therefore climate changes like rising sea levels are unrelated to greenhouse gas emissions (Figure 3)

Certain changes in climate conditions cannot be linked to greenhouse gas emissions

The overall pattern of change in sea levels will be influenced by the period of time over which the data is collected

While sea levels did increase preceding the industrial revolution, this rise in sea levels followed a preceding period of decrease

The rate at which sea levels have risen in the past 30 years is greater than that seen in the last 200 years

Three different models of predicted climate change commissioned by the IPCC show variation of more than 5ºC (Figure 4)

Climate change models are based on assumptions and if those assumptions are false, the predictions will be incorrect

The assumptions made by the different models relate to the extent of human activity predicted over the next 100 years

Model A1B predicts a continued reliance on fossil fuels while model B1 predicts a reduction in the current use of raw materials

All three models still predict an increase in average global temperatures over the next 100 years

As of 2009, there were only ~39 molecules of carbon dioxide per 100,000 molecules in the atmosphere

At our current rate of CO2 emission, it will take mankind another 5 years to raise that level by 1 molecule (to 40 per 100,000)

While we may double atmospheric CO2 levels by the end of the century, doubling a small number still produces a small number

The reason why carbon dioxide is so important to the environment is because there is so little of it

Living things require constant internal environments (homeostasis) – small external changes can have big impacts on viability