Cambridge Global English Activity Book 1 Answers Pdf

[Kayleigh Telega]

Everysingle year since 1977 has been warmer than the 20th century average. Nineteen of the 20 warmest years have occurred since 2001. The period of 2015 to 2019 included the top five hottest years on record.

Analysis of these trends strongly suggests that without the emissions from burning coal and oil, it is very unlikely that 13 out of the 15 warmest years on record would have occurred either on their own or in such quick succession. This also makes sense from the known causes.

The answer is in the science. The CO2 produced from fossil fuels carries a unique signature that differentiates it from CO2 produced from other sources. In brief, it carries a specific ratio of carbon isotopes that is only found in the atmosphere when coal, oil, or gas is burned.

Within the scientific community, there is essentially no disagreement on the causes of climate change. Multiple studies have shown that at least 97 percent of scientists agree that global warming is happening and that human activity is the primary cause.

For example, in a landmark 2004 paper, researchers determined that climate change had at least doubled the risk of occurrence of the record-breaking 2003 European summer heat wave, which resulted in the deaths of tens of thousands of people. A 2016 study of the same heat wave concluded that human-caused climate change had increased the risk of heat-related mortality during the event by about 70 percent in central Paris and about 20 percent in London.

While some types of events are more readily attributable to global warming than others, attribution science is becoming increasingly robust. Several authoritative scientific institutions and government agencies have confirmed both the rigor and the validity of attributing individual extreme events to human-caused climate change.

Knowing that human activities are the main driver of global warming helps us understand how and why our climate is changing, and it clearly defines the problem as one that is within our power to address.

What does that mean? It means investing in a clean energy economy and healthier and more livable and resilient communities. It means transforming transportation, reorienting our food system, and shifting to lower-carbon lifestyles. It means battling the disinformation spread by fossil fuel companies and other wealthy interests. And it means fighting for equity and environmental justice for all.

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Carbon flows between each reservoir in an exchange called the carbon cycle, which has slow and fast components. Any change in the cycle that shifts carbon out of one reservoir puts more carbon in the other reservoirs. Changes that put carbon gases into the atmosphere result in warmer temperatures on Earth.

This diagram of the fast carbon cycle shows the movement of carbon between land, atmosphere, and oceans. Yellow numbers are natural fluxes, and red are human contributions in gigatons of carbon per year. White numbers indicate stored carbon. (Diagram adapted from U.S. DOE, Biological and Environmental Research Information System.)

Only 80 percent of carbon-containing rock is currently made this way. The remaining 20 percent contain carbon from living things (organic carbon) that have been embedded in layers of mud. Heat and pressure compress the mud and carbon over millions of years, forming sedimentary rock such as shale. In special cases, when dead plant matter builds up faster than it can decay, layers of organic carbon become oil, coal, or natural gas instead of sedimentary rock like shale.

Chemistry regulates this dance between ocean, land, and atmosphere. If carbon dioxide rises in the atmosphere because of an increase in volcanic activity, for example, temperatures rise, leading to more rain, which dissolves more rock, creating more ions that will eventually deposit more carbon on the ocean floor. It takes a few hundred thousand years to rebalance the slow carbon cycle through chemical weathering.

However, the slow carbon cycle also contains a slightly faster component: the ocean. At the surface, where air meets water, carbon dioxide gas dissolves in and ventilates out of the ocean in a steady exchange with the atmosphere. Once in the ocean, carbon dioxide gas reacts with water molecules to release hydrogen, making the ocean more acidic. The hydrogen reacts with carbonate from rock weathering to produce bicarbonate ions.

The time it takes carbon to move through the fast carbon cycle is measured in a lifespan. The fast carbon cycle is largely the movement of carbon through life forms on Earth, or the biosphere. Between 1015 and 1017 grams (1,000 to 100,000 million metric tons) of carbon move through the fast carbon cycle every year.

The bonds in the long carbon chains contain a lot of energy. When the chains break apart, the stored energy is released. This energy makes carbon molecules an excellent source of fuel for all living things.

Plants and phytoplankton are the main components of the fast carbon cycle. Phytoplankton (microscopic organisms in the ocean) and plants take carbon dioxide from the atmosphere by absorbing it into their cells. Using energy from the Sun, both plants and plankton combine carbon dioxide (CO2) and water to form sugar (CH2O) and oxygen. The chemical reaction looks like this:

Four things can happen to move carbon from a plant and return it to the atmosphere, but all involve the same chemical reaction. Plants break down the sugar to get the energy they need to grow. Animals (including people) eat the plants or plankton, and break down the plant sugar to get energy. Plants and plankton die and decay (are eaten by bacteria) at the end of the growing season. Or fire consumes plants. In each case, oxygen combines with sugar to release water, carbon dioxide, and energy. The basic chemical reaction looks like this:

In all four processes, the carbon dioxide released in the reaction usually ends up in the atmosphere. The fast carbon cycle is so tightly tied to plant life that the growing season can be seen by the way carbon dioxide fluctuates in the atmosphere. In the Northern Hemisphere winter, when few land plants are growing and many are decaying, atmospheric carbon dioxide concentrations climb. During the spring, when plants begin growing again, concentrations drop. It is as if the Earth is breathing.

The ebb and flow of the fast carbon cycle is visible in the changing seasons. As the large land masses of Northern Hemisphere green in the spring and summer, they draw carbon out of the atmosphere. This graph shows the difference in carbon dioxide levels from the previous month, with the long-term trend removed.

This cycle peaks in August, with about 2 parts per million of carbon dioxide drawn out of the atmosphere. In the fall and winter, as vegetation dies back in the northern hemisphere, decomposition and respiration returns carbon dioxide to the atmosphere.

Left unperturbed, the fast and slow carbon cycles maintain a relatively steady concentration of carbon in the atmosphere, land, plants, and ocean. But when anything changes the amount of carbon in one reservoir, the effect ripples through the others.

Without human interference, the carbon in fossil fuels would leak slowly into the atmosphere through volcanic activity over millions of years in the slow carbon cycle. By burning coal, oil, and natural gas, we accelerate the process, releasing vast amounts of carbon (carbon that took millions of years to accumulate) into the atmosphere every year. By doing so, we move the carbon from the slow cycle to the fast cycle. In 2009, humans released about 8.4 billion tons of carbon into the atmosphere by burning fossil fuel.

Emissions of carbon dioxide by humanity (primarily from the burning of fossil fuels, with a contribution from cement production) have been growing steadily since the onset of the industrial revolution. About half of these emissions are removed by the fast carbon cycle each year, the rest remain in the atmosphere. (Graph by Robert Simmon, using data from the Carbon Dioxide Information Analysis Center and Global Carbon Project.)

All of this extra carbon needs to go somewhere. So far, land plants and the ocean have taken up about 55 percent of the extra carbon people have put into the atmosphere while about 45 percent has stayed in the atmosphere. Eventually, the land and oceans will take up most of the extra carbon dioxide, but as much as 20 percent may remain in the atmosphere for many thousands of years.

The changes in the carbon cycle impact each reservoir. Excess carbon in the atmosphere warms the planet and helps plants on land grow more. Excess carbon in the ocean makes the water more acidic, putting marine life in danger.

Rising concentrations of carbon dioxide are warming the atmosphere. The increased temperature results in higher evaporation rates and a wetter atmosphere, which leads to a vicious cycle of further warming. (Photograph 2011 Patrick Wilken.)

So while carbon dioxide contributes less to the overall greenhouse effect than water vapor, scientists have found that carbon dioxide is the gas that sets the temperature. Carbon dioxide controls the amount of water vapor in the atmosphere and thus the size of the greenhouse effect.

Rising carbon dioxide concentrations are already causing the planet to heat up. At the same time that greenhouse gases have been increasing, average global temperatures have risen 0.8 degrees Celsius (1.4 degrees Fahrenheit) since 1880.

With the seasonal cycle removed, the atmospheric carbon dioxide concentration measured at Mauna Loa Volcano, Hawaii, shows a steady increase since 1957. At the same time global average temperatures are rising as a result of heat trapped by the additional CO2 and increased water vapor concentration. (Graphs by Robert Simmon, using CO2 data from the NOAA Earth System Research Laboratory and temperature data from the Goddard Institute for Space Studies.)

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