To decrease the bitterness, bring out the sweetness in the carrots by cooking for longer.
The best technique I've found to do this with carrots is frying and steaming them at a low temperature.
Make glazed carrots: per 200g of carrot, peel, cut into ~2cm thick diagonal cuts and add 40g butter, a half teaspoon of sugar and season with salt and black pepper.
In a large lidded pan over a low heat, spread the carrots out in a single layer, add the lid and cook for 25-35 minutes.
Shake the pan occasionally.
Push the cooking time as long as you can without letting the carrots become overly soft.
This should give deliciously sweet fragrant carrot.
Another thing to keep in mind is that salt is better than sugar to reduce bitterness so add as much as you can without oversalting the carrots.
cooking.stackexchange.com/users/8690/jcorcoran
Make cole slaw with them, and some zucchini and parsnips, then dress with mayo, red wine vinegar and apple cidar vinegar.
Gradually add some white sugar to take the edge off of any remaining bitterness.
This palate will balance out the bitter and play it up with the sharpness of the parsnips.
Zucchini, when shredded finely and left in a mayo/vinegar dressing will soften to an almost shredded cheese texture and turn into the median flavor distracting from over bitter carrots.
I had a large bag of zucchini that was on its way out recently, and some carrots that had since passed the point of just being white and were no longer right enough to eat raw anymore.
This extended their (fridge) shelf lives in one swoop.
cooking.stackexchange.com/users/15/mfg
Some varieties are naturally high in terpenoids, which make the carrots taste bitter.
Because terpenoids develop earlier than sugars, a carrot that is harvested too young might taste bitter.
if you're growing them yourself make sure you wait a little longer before harvesting.
And if you're buying them you'll have to cook them.
I love myself some raw carrots but end up throwing out bags sometimes because they're bitter.
Goodluck.
cooking.stackexchange.com/users/78518/Danielle Folk
Whatever you do, you should cook the carrots.
Carrots usually become sweeter when cooked.
And you can alter the flavor slightly by cooking in a broth, sauce, roasting with other ingredients, etc.
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I'm thinking stock or compost. :)
cooking.stackexchange.com/users/7882/Trin
I've got a bunch of two week old carrots (kept in the fridge), peeled, and they tasted bitter (raw).  Is it normal that carrots turn bitter?  Is there a way to prevent it from happening?  Will the taste improve after cooking? (I'll cook and taste anyway)  I've looked at  this question , but the peel is said to be bitter, while these are peeled already.
What can be done with bitter carrots?
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<storage-lifetime><carrots>
cooking.stackexchange.com/questions/18781
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Some varieties are naturally high in terpenoids, which make the carrots taste bitter. Often cooking them will bring out the sweetness. Some carrots are more bitter than others. Cooking them should bring out their sweetness.
Cooking the carrots should bring out their sweetness. Some carrot varieties are more bitter than others.