If Iceland's Katla Volcano awakens from slumber and erupts, Icelanders and air travelers won't be the only ones affected. Eruptions from large volcanoes have wreaked havoc on Earth's ecosystem by lowering temperatures and thinning the ozone layer.

Katla is a much bigger volcano than Eyjafjallajokull which spewed ash all over Europe for several weeks and grounded air travel across Northern Europe. The potential for a global disaster should Katla erupt is higher than Eyjafjallajokull. Gases released in a major eruption can cause increased coughing and eye and skin irritation that can lead to serious lung conditions. Ash which has sharp, jagged edges microscopically can get into lungs and airways and cause health conditions.

Another global effect of a volcanic eruption is a cool down in temperatures. Sulfur released from volcanic eruptions can cool the Earth. Sulfur can form sulfuric acid droplets than can block the sunlight hitting the Earth. These sulfur infused droplets can stay in the atmosphere for a year. Another Iceland volcano, Laki erupted in 1783 and caused extreme weather in Europe and contributed to a rise in respiratory diseases. If Katla erupts it can cause temperatures to lower worldwide. An eruption of Katla's magnitude could unintentionally have positive effects such as slowing global warming.

Volcanic eruptions can also lead to acid rain if the acid coating on volcanic ash is removed by rain. Acid rain can pollute local water supplies and cause damage to vegetation. Livestock will also be affected if they eat or digest ash, causing another massive livestock die-off like the one in 1918 when Katla erupted.

For now experts are still monitoring the situation with Katla. Iceland's Meteorological Office has warned the public not to panic.

"There are presently no measurable signs that an eruption of Katla is imminent; however, given the heightened levels of seismicity, the situation might change abruptly," the office said in a statement on its website.

Katla erupted almost a century ago. The volcano averages two eruptions every 100 years raising fears that another one is about to hit.