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Earth, Climate, and Change

Observing Human Impact

What Is the Evidence?

Learning Targets

  • I can use photographs to observe changes over time and make inferences on the effects of these changes.
  • I can ask questions about the evidence of change that is altering the global climate.


Weather changes and overall climate can vary between warm and cool periods; however, average global temperatures have unquestionably risen in the last 100 years. Photographs can record how the effects of small changes in temperature will, over time, result in dramatic changes in oceans, coastlines, and other habitats. Photographs are essential for recording these changes because they might occur slowly, with variation over months or years that obscures a definite overall trend. For example, because coral reefs grow slowly, changes to their structure or composition are difficult to observe day to day. The same slow alterations occur to polar caps, glaciers, and sea level. Over time, however, these small changes add up to a noticeable difference. In this activity, students will use photos taken of a single location at different times to look for evidence of climate change.

Climate scientists have overwhelming evidence that human activities are affecting our climate, mainly through increased production of greenhouse gases such as methane and carbon dioxide (CH4 and CO2). Many sources generate these gases, including normal metabolism. Humans exhale CO2, and several types of bacteria generate CH4. Burning fossil fuels also generates greenhouse gases, however, and our use of petroleum-based fuels and the amount of greenhouse gases in the atmosphere have increased dramatically since the nineteenth century. Greenhouse gases re-radiate heat, raising atmospheric temperatures. Higher temperatures increase the amount of water that evaporates from oceans into the air. This affects land conditions as precipitation patterns change, potentially leading to floods or droughts.

Although we sometimes think of climate change as affecting only summer temperatures, in many ecosystems, warming winters also severely affect plants, animals, and humans. For example, increased atmospheric moisture makes snowstorms more severe. A lack of freezing days can cause infestations of insects that would normally be killed by freezing temperatures.

Another consequence of climate change is rising sea levels because of several factors, including higher water temperatures, and increased volume as water that is trapped as ice sheets and glaciers melts. When sea levels are higher, islands and coastal regions are more seriously affected by storm surges and, on an everyday basis, by encroaching salt water that changes habitats. Plants, animals, and microorganisms that are adapted to particular environmental conditions must adapt or change habitats to survive. Changing habitats affect conditions for humans, such as our supply of food and water.

Begin the Activity


  • Paper
  • Pencils or pens

In pairs or small groups, give students a series of photographs of the same location taken at different times. Have students observe, and then list and describe all the features in each photograph. Have them pay particular attention to anything that changed or anything that is exactly the same in the photos.

Once they have generated a list, have the students mark the list for items that changed and items that did not change in the photo series. Have the students use the list to draw a Venn diagram. One circle will list items in the earlier photo, with their descriptions, that look different from items in the later photo. The other circle will list items in the later photo, with descriptions, that look different from the earlier photo. The intersection will list items that appear the same in both photos. (So the nonintersecting parts might list the same items—such as a mountain or a rock—but will have different descriptions for those items, such as snow-covered or bare. The intersecting part will have items that have the same descriptions for both photos, such as a rocky ridge with a little snow.)

Optional, advanced, or group discussion example: Photo 3516 show photos before and after Hurricane Sandy, a particularly strong hurricane in 2012. Although an individual hurricane might seem like an isolated event, increased atmospheric moisture can make storms more severe.

When all the teams are finished, have them share their results with the class. Ask guiding questions and bring up discussion questions about key points in each set.

Questions to Consider

  • What might be the impact of these changes beyond what is in the photo?
  • What changes might be disruptive for wildlife habitats, vegetation, or human communities?
  • What ways can you think of to reduce the disruptive effects of the changes you observed?
    • Suggested activity for this question: Have students make a two-column table with pros and cons of trying to reduce a disruptive effect of climate change. For example, if students think of building a dam to prevent floods, a good exercise might be writing down the upstream effects of a dam.
  • Optional question if your class has covered material on Earth’s Systems (ES22): What might be the scientific basis for any changes your team noted in the earlier and later photographs?

Students’ answers will vary depending on the set of photos they received. Their answers should reflect the changes they have already noticed and what will happen if those changes continue.

For example, if they noticed that the amount of water in an area has increased over time, they might say that the area is likely to continue flooding, and people who live in the area will have to move.

They might note that coral reef death affects species that depend on coral habitats. (Coral bleaching, which is loss of the algae that live in coral tissues, occurs when water is too warm and can lead to death of the coral.)

They might note that flooding could continue if warmer temperatures result in increased water evaporation, leading to the heavy rainfall that causes flooding. In contrast, increased evaporation in places that are normally dry results in droughts. Other impacts include heat waves; warmer winters; changing ecosystems; a possible loss, decrease, or increase in species; and effects on agriculture from drought, heat, and floods.

Anything that causes changes in the ecosystem is likely to be disruptive to wildlife. For example, flooding will disrupt a habitat for any wildlife living in the flooded area. Students might note that, although humans often have the technology to help them live in changing conditions, severe changes, such as extreme flooding or drought, might cause people to move from a community.

next: Where Does the Water Go? A Global Journey

Grade Level

Middle & High School


Earth and Space Science
Environmental Studies
Physical Science
Social Studies


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