Last Glacial Maximum

A long time ago, the Earth was very cold.

Huge sheets of ice covered much of the land. Because the ice held so much water, the sea was much lower.

This low sea let many lands join together. Most places became very dry and dusty. Large deserts grew in many parts of the world.

It was a very different and chilly world.

A long time ago, the Earth was very cold. This was the Last Glacial Maximum. It happened between 26,000 and 20,000 years ago.

Huge ice sheets covered much of North America and Europe. These ice sheets were very big. They also covered parts of Asia.

Because the ice held so much water, the sea level dropped. The sea was 125 meters lower than it is today.

This low sea joined many lands together. In Asia, islands joined the main land. This area is called Sundaland. In the south, Australia and New Guinea joined too. We call this land Sahul.

The world was also very dry. Most deserts grew much larger. Many forests became grasslands. The air was very dusty. There was 20 to 25 times more dust than today.

This happened because there was less rain. Strong winds also moved the dust around. It was a very different world.

The Last Glacial Maximum was a very cold time on Earth. It was the most recent time when giant ice sheets were at their largest. This happened between 26,000 and 20,000 years ago.

These massive sheets of ice covered much of Northern North America, Northern Europe, and Asia. Because the ice held so much water, the sea level dropped a lot. The ocean was about 125 meters lower than it is today.

This change made the world look very different from what we see now.

This cold period worked by changing how water and air moved. To make an ice sheet, you need long periods of cold and lots of snow. As the ice grew, it locked up huge amounts of water from the oceans. This caused the sea levels to fall and exposed flat land called continental shelves.

The ice also changed the air. Large clouds formed over the oceans and reflected sunlight away. This made the planet even colder. The world became much drier because the water was stuck in ice instead of falling as rain.

Scientists use different clues to study this time. They look at things like ice cores and the types of fossils found in the ground. Archaeologist Jennifer French says this period began around 27,500 years ago. She notes the ice was at its biggest by 26,000 years ago.

In Britain, people call this time the Dimlington Stadial. It is dated between 31,000 and 16,000 years ago. Researchers often pick different dates based on the data they use to study the past.

Many places changed during the Last Glacial Maximum. Most deserts grew much larger during this time. In Australia, shifting sand dunes covered half of the entire continent.

The air was also very dusty. There was 20 to 25 times more dust in the air than there is today. This happened because there was less plant life and stronger winds. In some places, like the western United States, it actually rained more. This created large lakes like Lake Bonneville in Utah.

We can see how this connects to our world by looking at maps. When the sea level was low, many islands became part of the mainland. In Asia, islands like Borneo and Bali joined the continent to form Sundaland.

In the south, Australia, New Guinea, and Tasmania joined to form a landmass called Sahul. Today, the ocean has risen and separated these lands again. Learning about this helps us understand how our climate can change over long periods of time.

The Last Glacial Maximum (LGM) was the most recent period of peak ice coverage during the Last Glacial Period. This era occurred between 26,000 and 20,000 years ago. During this time, massive ice sheets stretched across much of Northern North America, Northern Europe, and Asia.

This period is also known as the Last Glacial Coldest Period. It profoundly reshaped the Earth's climate, geography, and biological landscapes. The LGM was characterized by much colder temperatures and significantly drier conditions across most of the globe.

To form these massive ice sheets, the Earth required two specific conditions: prolonged cold and heavy precipitation in the form of snow. As snow accumulated over long periods, it compressed into ice, growing into vast sheets. This process locked up enormous quantities of water that would otherwise be in the oceans. Consequently, the sea level dropped significantly, reaching about 125 meters (410 feet) lower than it is today.

This drop exposed continental shelves and created new coastal plains. The ice also altered atmospheric circulation. Large clouds formed over the cooling northern Pacific and Atlantic oceans. These clouds reflected sunlight back into space, which amplified the global cooling effect.

Different regions experienced the LGM in distinct ways. In the northern hemisphere, massive continental ice sheets dominated. However, East Asia remained largely unglaciated despite having cold temperatures. This happened because the ice sheets in Europe created extensive anticyclones, or large-scale weather systems, above them. These systems generated very dry air masses that reached Siberia and Manchuria. Because the air was so dry, there was not enough precipitation to form glaciers in most of Asia. Other factors, such as the relative warmth of the Pacific Ocean and large mountain ranges, also prevented continental glaciation there.

Researchers use various methods to determine when the LGM began and ended. They study terrestrial cosmogenic nuclides and radiocarbon dating to track ice sheet margins. Because different scientists use different data sets and criteria, there is no single agreed-upon timeline. For example, archaeologist Jennifer French dates the onset to 27,500 years ago. She suggests ice sheets reached their maximum by 26,000 years ago, with deglaciation starting between 20,000 and 19,000 years ago. In Britain, this period is called the Dimlington Stadial and is dated between 31,000 and 16,000 years ago.

The scale of change during the LGM was immense. The average global temperature about 21,000 years ago was approximately 6 °C colder than present-day levels. According to the USGS, permanent summer ice covered about 8% of the Earth's surface and 25% of the land area.

In contrast, today only about 3.1% of Earth's surface is covered in year-round ice. The atmosphere was also much dustier. Dust levels were 20 to 25 times higher than they are now. This was caused by reduced vegetation, stronger global winds, and less rain to clear the air.

Vegetation patterns shifted dramatically across the planet. Most deserts expanded, and many subtropical regions lost their forests to open woodlands. In Southern Australia, shifting sand dunes covered half of the continent.

The Amazon rainforest was split into two large blocks by extensive savanna. However, some areas experienced unexpected changes. In the western United States, changes in the jet stream brought heavy rain to areas that are now deserts. This created large pluvial lakes, such as Lake Bonneville in Utah. Similarly, a major lake formed in the Dasht-e Kavir in Afghanistan and Iran.

One of the most striking effects of the LGM was the connection of landmasses. Because the sea level was so low, many islands became part of the mainland. In Southeast Asia, the Indonesian islands like Borneo and Bali joined the continent to form a landmass called Sundaland.

In the southern hemisphere, the Australian mainland, New Guinea, and Tasmania joined to form Sahul. These connections allowed for different patterns of movement and life across the globe. Understanding the LGM helps scientists study how the hydrological cycle and global temperatures interact to change the face of our world.