Phase changes notwithstanding, one of water's crucial aspects is its constancy. Regardless of its appearance, the total amount of water on or above the planet hardly changes. Some water vapor is lost to space and some water becomes "locked" into rocks, but to a surprising extent the quantity of water on Earth is constant. Water might change forms, appearing as ice, liquid water, or as water vapor; however, rain isn't new water. There is virtually no new water. Almost all the water that was, that is, and that will ever be has been present on this planet in one form or another for many millennia. In other words, some chemical processes aside, we drink the water the dinosaurs drank! That's right! Virtually all water has been warmed by the Sun innumerable times. It has fallen as rain over and over and over again. It has frozen into snow and ice almost as often.
The total amount of water on Earth does not change when the global climate
warms or cools, but the fraction of the water that is liquid, solid or
gas does change. So does the distribution of the water on the planet. For
example, at times when the global climate is cooler, more water might be
frozen as polar ice, leaving less liquid water in the oceans. During times
when the Earth's atmosphere warms up, the rate of evaporation increases,
and so does the amount of water vapor in the atmosphere. This increase
in humidity results in more clouds and hence more rain. During colder periods,
there is less evaporation and humidity is low, so there are fewer clouds
and less precipitation.
b. Devise strategies to speed the disappearance of a small puddle (2-3 drops) from a piece of waxed paper. Which strategies are predicted to work best? Which do?
c. Discuss the order in which water's changes in phase can occur. Draw a picture showing the three phases of water and connect the phases with arrows to show common transformations. Can vapor and solid be connected?
d. Scientists are working to understand how climate change might
affect the rates of natural processes such as evaporation. In their experiments,
comparatively normal conditions - generally called controls - are
compared to novel, or experimental, conditions. What would the control
condition be for a classroom experiment on evaporation? List good places
to simulate the experimental condition of a warm climate.
b. Label the sixteen cups: four "ice", four "snow", four "water", and four "wet earth".
c. Place one ice cube into each cup marked "ice".
d. Using the plastic bag and a hammer, crunch one ice cube. Place the resulting "snow" in one cup marked "snow". Repeat this procedure to fill each remaining cup marked "snow". Do not crush more than one ice cube at a time, as volume must be as close to identical as possible for later comparisons to be legitimate.
e. One at a time, pour one ice-tray section of water (having volume equivalent to one ice cube) onto each of the four cups marked "water".
f. Use the tablespoon to place the same amount of soil in each of the cups marked "wet earth", then add one ice-tray section of water to the soil. Mix the soil and water.
g, Group the cups into four sets of four, so that each group contains one cup of ice, one of snow, one of water, and one of wet earth. Place one set of cups in each of the location simulating control and experimental conditions. Make an initial observation of water level in each cup, and record the experiment's starting time.
h. Once an hour (or at other pre-arranged times), check how much
water remains in each cup. Record how long it takes for each cup to dry
out completely. Check the soil for moisture by blotting it with the filter
paper and looking for signs of wetness.
b. How might rates of evaporation be speeded?
c. What could happen to evaporation rates in the event of global warming?
d. How have ice caps at the North and South poles continued to exist in the face of past periods of warming?
e. Besides increased evaporation and resultant precipitation,
what other consequences of global warming might arise?