Uploaded September 2026 | Updated September 2026, 17 minutes ago
Earth has been dramatically hotter—and colder—than it is today. So what can 450 million years of climate history tell us about where we're headed next? Paleoclimatologist Dr. Jessica Tierney explains how scientists use Earth's ancient climates to test climate models and understand the consequences of rising CO₂.
From Antarctic ice cores containing ancient air to tree rings, corals, ocean sediments and even plant wax preserved for millions of years, paleoclimate records provide a window into climates humans have never experienced. Tierney explains what these records reveal about climate sensitivity, extreme heat, drought, rainfall and the future of the American West.
The lecture also explores a surprising possibility: although warming drives greater soil moisture loss in the Southwest, ancient evidence suggests the North American monsoon could become stronger under certain warmer conditions. Tierney also examines the Pliocene, the Eocene and nearly 500 million years of Earth's climate history—and explains why saying "Earth has been hotter before" misses the most important point: the unprecedented rate of modern warming.
ABOUT THE SPEAKER
Dr. Jessica Tierney is a paleoclimatologist whose research uses geological evidence and climate modeling to reconstruct Earth's past climates and understand future climate change. Her work examines ancient temperature, precipitation, atmospheric CO₂, climate sensitivity and regional hydroclimate, including the North American monsoon. In this lecture, she discusses research spanning the last Ice Age, the Pliocene and Eocene warm periods, and a reconstruction reaching more than 450 million years into Earth's climate history.
WHY THE PAST MATTERS
Ancient climates give scientists something future projections cannot: known outcomes against which climate models can be tested. By "hindcasting" climates that already happened, researchers can determine which models realistically reproduce Earth's response to major changes in CO₂—and improve predictions of what may happen next.
CHAPTERS
0:00 Introduction: Studying Ancient Climate Change
3:30 Rising CO₂ and Modern Global Warming
8:30 Extreme Weather and Climate Change
13:00 How Scientists Reconstruct Ancient Climates
18:30 Ice Cores and 800,000 Years of CO₂
23:00 What Is Climate Sensitivity?
28:30 Testing Climate Models Against the Past
34:00 The Eocene Greenhouse World
39:30 What the Ice Age Reveals
44:00 Drought and the Colorado River
49:30 Will the Southwest Monsoon Change?
54:30 The Leaf-Wax Monsoon Gauge
1:00:00 The Pliocene as a Future Climate Analog
1:06:00 450 Million Years of Earth's Climate
1:11:30 Earth Was Hotter—So Why Worry?
1:16:00 Audience Q&A
#ClimateChange #ClimateScience #GlobalWarming #Paleoclimatology #EarthScience
Earth has been dramatically hotter—and colder—than it is today. So what can 450 million years of climate history tell us about where we're headed next? Paleoclimatologist Dr. Jessica Tierney explains how scientists use Earth's ancient climates to test climate models and understand the consequences of rising CO₂.
From Antarctic ice cores containing ancient air to tree rings, corals, ocean sediments and even plant wax preserved for millions of years, paleoclimate records provide a window into climates humans have never experienced. Tierney explains what these records reveal about climate sensitivity, extreme heat, drought, rainfall and the future of the American West.
The lecture also explores a surprising possibility: although warming drives greater soil moisture loss in the Southwest, ancient evidence suggests the North American monsoon could become stronger under certain warmer conditions. Tierney also examines the Pliocene, the Eocene and nearly 500 million years of Earth's climate history—and explains why saying "Earth has been hotter before" misses the most important point: the unprecedented rate of modern warming.
ABOUT THE SPEAKER
Dr. Jessica Tierney is a paleoclimatologist whose research uses geological evidence and climate modeling to reconstruct Earth's past climates and understand future climate change. Her work examines ancient temperature, precipitation, atmospheric CO₂, climate sensitivity and regional hydroclimate, including the North American monsoon. In this lecture, she discusses research spanning the last Ice Age, the Pliocene and Eocene warm periods, and a reconstruction reaching more than 450 million years into Earth's climate history.
WHY THE PAST MATTERS
Ancient climates give scientists something future projections cannot: known outcomes against which climate models can be tested. By "hindcasting" climates that already happened, researchers can determine which models realistically reproduce Earth's response to major changes in CO₂—and improve predictions of what may happen next.
CHAPTERS
0:00 Introduction: Studying Ancient Climate Change
3:30 Rising CO₂ and Modern Global Warming
8:30 Extreme Weather and Climate Change
13:00 How Scientists Reconstruct Ancient Climates
18:30 Ice Cores and 800,000 Years of CO₂
23:00 What Is Climate Sensitivity?
28:30 Testing Climate Models Against the Past
34:00 The Eocene Greenhouse World
39:30 What the Ice Age Reveals
44:00 Drought and the Colorado River
49:30 Will the Southwest Monsoon Change?
54:30 The Leaf-Wax Monsoon Gauge
1:00:00 The Pliocene as a Future Climate Analog
1:06:00 450 Million Years of Earth's Climate
1:11:30 Earth Was Hotter—So Why Worry?
1:16:00 Audience Q&A
#ClimateChange #ClimateScience #GlobalWarming #Paleoclimatology #EarthScience
