Sea change na podstawie https://climate.nasa.gov/climate_resourc

Sea level has remained fairly constant throughout Earth's history.

• True

• False

Answer explanation

Over long geological timescales, changes in the shape of the ocean basins and in land-sea distribution affect sea level. During the past few million years' ice age cycles, sea level has varied by more than a hundred meters. However, according to a reconstruction by Kemp et al. 2011, 20th century sea-level rise on the U.S. Atlantic coast is faster than at any time in the past two thousand years.

What percentage of heat from global warming has the ocean absorbed in the past 40 years?

• 11%

• 35%

• 90%

Answer explanation

Water resists changes in temperature; it is slow to heat up and slow to cool down. In scientific terms, water has high heat capacity. This means that, so far, Earth's ocean has been able to absorb and hold a majority of the heat from Earth's atmosphere.

Melting sea ice has the potential to raise sea level by several meters.

• True

• False

Answer explanation

Melting sea ice cannot raise global sea level since the ice is already floating. (Think of an ice cube melting in a glass full of water.) However, Arctic sea ice is thinning and the long-term summer average has decreased by 34 percent since 1979. Ice from glaciers and ice sheets, which form on land, does add water to Earth's ocean when it melts and does contribute to sea level rise.

The normal temperature range for ocean surface water is:

• -2 to 40°C

• -5 to 50°C

• 4.5 to 18°C

• -2 to 35°C

Answer explanation

Very cold and very salty water sinks to become deep water in Earth's polar regions, while warm water tends to remain on the surface in tropical waters. Fresh water freezes at 0°C, but sea water freezes at colder temperatures because it contains salt.

What percentage of the world's population lives within 100 kilometers of the shoreline?

• about 30%

• about 60%

• about 70%

Answer explanation

According to the World Resources Institute, in 1995 2.2 billion people, or 39 percent of the world's population, lived on or within 100 kilometers of a seashore. Recent studies reveal that up to 600 million people live in Low Elevation Coastal Zones and 200 million people live within coastal flood plains.

Sea level rise contributes to more frequent flooding in which of these coastal areas?

• Venice, Italy

• Tuvalu

• Bangladesh

• All of the above

Answer explanation

Tuvalu, a small island nation in the Pacific Ocean, is only 4.5 meters above sea level at its highest point. Rising sea level and high tides could submerge it entirely. Bangladesh is affected by yearly monsoonal flooding in addition to sea level rise. Venice becomes inundated because the land is gradually sinking by about 10 centimeters per year, an effect exacerbated by sea level rise.

El Niño is the result of global warming.

• True

• False

Answer explanation

El Niño is a natural Earth system phenomenon and is not directly associated with, or caused by, global warming. El Niño, marked by episodes of warm water in the eastern Pacific, is associated with regional and global changes in precipitation and ocean circulation patterns and has been occurring for hundreds of years or more. However, climate change might be influencing its frequency and intensity. Observations show that El Niño, La Niña and El Niño–Southern Oscillation (ENSO)-neutral years all display a long-term warming trend up to the present.

Other than melting land-based ice sheets, which of these factors has made the largest contribution to the rise in sea level over the past 100 years?

• Warming of ocean surface waters

• Melting sea ice

• Increased river runoff

Answer explanation

As the ocean warms, it expands and sea level rises, accounting for about a third of the approximately 20-centimeter sea-level rise seen in the past century. Water released by melting land-based ice sheets contributes the other two-thirds of sea level rise.

The leading cause of coral bleaching over the past 20 years is:

• Runoff and pollutants

• Overexposure to sunlight

• Rising ocean temperatures

• Low tides

Answer explanation

The leading cause of coral bleaching is rising ocean temperatures due to climate change. Although runoff and pollutants, sunlight, and low tides can impact coral, those impacts normally occur near the shoreline in shallow waters.

The acidity of a substance is measured using the pH scale. Ocean water has a pH of approximately 8. That means ocean water is fairly neutral — and slightly basic. However, in the past 100-200 years, scientists have observed that ocean water has become approximately what percent more acidic due to human greenhouse gas emissions?

• 40%

• 30%

• 5%

• 10%

Answer explanation

Many human activities — such as exhaust from cars and factories — release a gas called carbon dioxide into the air. Extra carbon dioxide gas in the atmosphere is absorbed by the ocean, making the water more acidic. Acids can break down the shells of animals that live in the sea. Because ocean water has become more acidic, some animals — like certain oysters and clams — are increasingly having difficulty in making or keeping their shells. These negative impacts are projected to worsen.