3.3 Modern climate change

Learning objectives

After reading this module, students should be able to

• assess long-term global temperature records and place recent climate change into the context of historical temperature observations
• explain how changes in the Sun's energy output have impacted the last 1300 years of global temperature records
• analyze the human impact on the planetary albedo and relate these changes to recent climate change
• predict the response of the global average temperature when large volcanic eruptions occur
• explain the enhanced greenhouse effect
• discuss how recent observations of change measured within regional ecosystems are related to global climate change

Introduction

In previous modules, an examination of the geologic record of the earth’s climate in the Quaternary Period revealed the primary drivers of climate change. The most important conclusions to be drawn from the Modules Climate Processes; External and Internal Controls and Milankovitch Cycles and the Climate of the Quaternary are the following:

1. In the past, Earth has been significantly warmer (and mostly ice free) and significantly colder (especially during the so-called “Snowball Earth” eras) than it is today.
2. Climate change occurs when there are changes in insolation, albedo, and composition of the atmosphere.
3. Climate is the average of weather, and changes to the earth’s climate occur on long time scales.

Recent climate change, which has occurred during the modern instrument era, is the focus of this module. It is through the lens of long-term climate change (occurring on thousands to millions of years) that we will view earth’s current climate and recent climate change. The goal is to investigate how the principles listed above are shaping current climate events.

Mechanisms

Temperature records

Figure Northern Hemisphere Surface Air clearly shows that the current global average temperature reflects an interglacial warm period. If we focus in on the end of this record we can observe some of the fine scale changes in the global temperature records. Figure Northern Hemisphere Surface Air combines proxy data (i.e., information from ice cores and tree rings) with the modern instrument record to create a graph showing the last 1300 years of Northern Hemisphere (hereafter, NH) temperatures. Each line on the top two panels represents a different temperature data set collected in the NH and the bottom panel color codes the percentage of overlap among these data sets.