6.5 Conservation, Human Impacts, and Climate Change

Why Conservation and Climate Change Matter for the Praxis Biology Exam

The Praxis Biology exam includes items on human impacts, the major threats to biodiversity, climate change mechanisms, and conservation strategies. Expect a question that tests the HIPPO acronym, an item on the greenhouse effect or ocean acidification, and an item asking you to distinguish in-situ from ex-situ conservation. Teachers must be able to explain these mechanisms accurately and cite primary sources like the IPCC and the EPA.

HIPPO: The Six Major Threats to Biodiversity

E.O. Wilson popularized the HIPPO mnemonic to rank the leading drivers of species loss, with the original five letters often extended to include climate change.

Climate change is increasingly treated as a sixth major threat, sometimes folded into a HIPPOC or HIPPCO acronym. According to the IPCC AR6 Working Group II report (2022), climate change is now a dominant driver of species range shifts and is projected to threaten more species than habitat loss within decades.

The Greenhouse Effect and Climate Change

The greenhouse effect is a natural process. Without it, Earth's average surface temperature would be about -18 deg C; with it, average surface temperature is about +15 deg C. Greenhouse gases (CO2, CH4, N2O, water vapor) absorb infrared radiation re-emitted by Earth's surface and trap heat in the lower atmosphere.

Human activities - fossil fuel combustion, deforestation, cement production, and agriculture - have intensified this effect. According to the IPCC Sixth Assessment Report (AR6, 2021-2023):

• Atmospheric CO2 reached approximately 420 ppm in 2024, roughly 50% above the pre-industrial level of 280 ppm.
• Global mean surface temperature has risen approximately 1.1 deg C since 1850-1900.
• It is unequivocal that human influence has warmed the atmosphere, ocean, and land.

The Keeling Curve

The Keeling curve is the continuous record of atmospheric CO2 measured at the Mauna Loa Observatory in Hawaii since 1958 by Charles David Keeling and the Scripps Institution of Oceanography (with NOAA). Two features are exam-relevant:

1. A long-term upward trend showing CO2 rising every year.
2. A seasonal sawtooth showing slight CO2 drops each Northern Hemisphere summer (when forests photosynthesize) and rises each winter (when respiration dominates).

The Keeling curve is one of the most cited datasets in climate science.

Ocean Acidification

About 30% of human-emitted CO2 dissolves into the oceans, where it reacts with seawater to form carbonic acid:

CO2 + H2O <-> H2CO3 <-> H+ + HCO3-

Excess H+ lowers ocean pH (more acidic). Ocean surface pH has dropped from approximately 8.2 to 8.1 since the Industrial Revolution - a roughly 30% increase in hydrogen ion concentration on the logarithmic pH scale (NOAA Ocean Acidification Program). Acidification dissolves calcium carbonate shells, harming corals, mollusks, and pteropods, and threatens entire marine food webs.

Biological Responses to Climate Change

Two responses appear repeatedly on the Praxis exam:

• Range shifts - species are moving toward higher latitudes and elevations as their climate envelopes shift. Many North American bird species have shifted ranges hundreds of kilometers northward in recent decades.
• Phenology mismatches - the timing of biological events (flowering, hatching, migration, emergence) is shifting at different rates among interacting species. When predators arrive too late for prey hatches, or pollinators emerge before flowers bloom, mutualisms collapse.

Conservation Strategies

In-situ conservation is generally preferred because it preserves ecological interactions and evolutionary processes; ex-situ serves as insurance and supports reintroduction programs. Wildlife corridors address the negative effects of habitat fragmentation by reconnecting isolated populations.

Restoration Ecology

Restoration ecology is the science of repairing degraded ecosystems. Common interventions include reintroducing native species, removing invasives, restoring hydrology (e.g., the Everglades restoration), and reestablishing fire regimes in fire-adapted systems like longleaf pine forests. Successful restoration depends on understanding the original community composition and the disturbance regime that maintained it.

Sustainable Development

Defined by the 1987 Brundtland Commission as development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Pillars include economic, social, and environmental sustainability. The United Nations Sustainable Development Goals (SDGs), adopted in 2015, provide a framework that schools and curricula increasingly reference.

Key U.S. and International Policy Touchstones

• Endangered Species Act (1973) - the foundational U.S. law protecting species listed as endangered or threatened; administered by the U.S. Fish and Wildlife Service and NOAA Fisheries. Bald eagles and American alligators are well-known recovery successes.
• Clean Air Act (1970) and Clean Water Act (1972) - reduced air and water pollutants nationwide; enforced by the U.S. EPA.
• Montreal Protocol (1987) - phased out ozone-depleting chlorofluorocarbons (CFCs); often cited as the most successful environmental treaty.
• Convention on International Trade in Endangered Species (CITES, 1973) - regulates international wildlife trade.
• IPCC reports - synthesize global climate science approximately every 7 years. The Sixth Assessment Report (AR6) was released between 2021 and 2023; the Seventh Assessment cycle is underway.

The Praxis often asks teachers to connect a real-world example (a bald eagle recovery, a coral bleaching event) to the underlying mechanism (DDT biomagnification, ocean warming) and the relevant policy or conservation approach.