Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 1
Executive Summary
By the end of this century, without a reduction in emissions, atmo -
spheric CO2 is projected to increase to levels that Earth has not experi-
enced for more than 30 million years. Critical insights to understanding
how Earth’s systems would function in this high-CO2 environment are
contained in the records of warm periods and major climate transitions
from Earth’s geological past.
Throughout its long geological history, Earth has had two fundamen-
tally different climate states—a cool “icehouse” state characterized by
the waxing and waning of continental-based ice sheets at high latitudes,
and a “greenhouse” state characterized by much warmer temperatures
globally and only small—or no—ice sheets. Although Earth has been in
an icehouse state throughout the time that humans evolved and for the
previous 30 million years, Earth has been in the warmer greenhouse state
for most of the past 600 million years of geological time.
As greenhouse gas emissions propel Earth toward a warmer climate
state, an improved understanding of climate dynamics in warm envi-
ronments is needed to inform public policy decisions. Research on the
climates of Earth’s deep past can address several questions that have
direct implications for human civilization: How high will atmospheric
CO2 levels rise, and how long will these high levels persist? Have sci -
entists underestimated the sensitivity of Earth’s surface temperatures to
dramatically increased CO2 levels? How quickly do ice sheets decay and
vanish, and how will sea level respond? How will global warming affect
rainfall and snow patterns, and what will be the regional consequences
for flooding and drought? What effect will these changes, possibly involv-
1
OCR for page 2
2 UNDERSTANDING EARTH’S DEEP PAST
ing increasingly acidic oceans and rapidly modified continental climates,
have on regional and global ecosystems? Because of the long-lasting
effects of this anthropogenic perturbation on the climate system, has per-
manent change—from a human point of view—become inevitable? How
many thousands of years will it take for natural processes to reverse the
projected changes?
The importance of these questions to science and to society prompted
the National Science Foundation, the U.S. Geological Survey, and Chevron
Corporation to commission the National Research Council to describe the
existing understanding of Earth’s past climates, and to identify focused
research initiatives to better understand the insights that the deep-time
record offers into the response of Earth systems to projected future climate
change. Throughout this report, “deep time” refers to that part of Earth’s
history that must be reconstructed from rock, and is older than historical
or ice core records. Although the past 2 million years of the Pleistocene
are included in “deep time,” most of the focus of the research described
or called for in this report is on the long record of Earth’s history prior to
the Pleistocene.
Although deep-time greenhouse climates are not exact analogues for
the climate of the future, past warm climates—and particularly abrupt
global warming events—provide important insights into how physical,
biogeochemical, and biological processes operate under warm condi-
tions. These insights particularly include the role of greenhouse gases
in causing—or “forcing”—global warming; the impact of warming on
ice sheet stability, sea level, and on oceanic and hydrological processes;
and the consequences of global warming for ecosystems and the global
biosphere. As Earth continues to warm, it may be approaching a critical
climate threshold beyond which rapid and potentially permanent—at
least on a human timescale—changes may occur, prompting major societal
questions: How soon could abrupt and dramatic climate change occur, and
how long could such change persist?
HIGH-PRIORITY DEEP-TIME CLIMATE RESEARCH AGENDA
The following six elements of a deep-time scientific research agenda
have the potential to address enduring scientific issues and produce excit-
ing and critically important results over the next decade:
• To understand how sensitive climates are to increased atmo -
spheric CO2.
• To understand how heat is transported around the globe and the
controls on pole-to-equator thermal gradients.
OCR for page 3
3
EXECUTIVE SUMMARY
• To understand sea level and ice sheet stability in a warm world.
• To understand how water cycles will operate in a warm world.
• To understand abrupt transitions across tipping points into a
warmer world.
• To understand ecosystem thresholds and resilience in a warming
world.
STRATEGIES AND TOOLS TO IMPLEMENT
THE RESEARCH AGENDA
Implementing the deep-time paleoclimate research agenda described
above will require four key infrastructure and analytical elements:
• Development of additional and improved estimates of precipita-
tion, seasonality, aridity, and soil productivity in the geological past.
• Continental and ocean drilling transects to collect high-resolution
records of past climate events and transitions, to determine climate
parameters before and after these events, and to model the dynamic pro -
cesses causing these transitions.
• Paleoclimate modeling focusing on past warm worlds and extreme
and/or abrupt climate events, at high resolution to capture regional paleo-
climate variability. Model outputs will be compared with climate records
from drilling transects and fine-tuned.
• A transition from single-researcher or small-group research efforts
to a much broader-based interdisciplinary collaboration of observation-
based scientists with climate modelers for team-based studies of important
paleoclimate events.
ENCOURAGING A BROADER COMMUNITY UNDERSTANDING
OF CLIMATES IN DEEP TIME
The public—and indeed many scientists—have minimal apprecia-
tion of the value of understanding deep-time climate history and appear
largely unaware of the relevance of far distant past times for Earth’s
future. The paleoclimate record contains surprising facts—there have
been times when the poles were forested rather than being icebound;
there were times when the polar seas were warm; there were times when
tropical forests grew at midlatitudes; more of Earth history has been
greenhouse than icehouse. Such straightforward concepts provide an
opportunity to help disparate audiences understand that the Earth has
archived its climate history and that this archive, while not fully under-
stood, is perhaps science’s best tool to understand Earth’s climate future.
OCR for page 4
4 UNDERSTANDING EARTH’S DEEP PAST
The possibility that our world is moving toward a “green-
house” future continues to increase as anthropogenic carbon
builds up in the atmosphere, providing a powerful motivation
for understanding the dynamics of Earth’s past “greenhouse”
climates that are recorded in the deep-time geological record.
An integrated research program—a deep-time climate research
agenda—to provide a considerably improved understanding of
the processes and characteristics over the full range of Earth’s
potential climate states offers great promise for informing indi-
viduals, communities, and public policy.
